Cross-linking molding process of high-toughness polyolefin composite leather material

Abstract

The application relates to the technical field of high polymer material processing, and discloses a cross-linking forming process of high-toughness polyolefin composite leather material, which comprises the following steps: heating calcined talcum powder, spraying active load liquid, adsorbing to obtain pre-impregnated talcum powder; heating, adding low-melting-point polyethylene wax, high-speed stirring, film forming to obtain a hot-state coating material; cooling and solidifying to obtain phase change master batches; low-temperature conveying and plasticizing the phase change master batches and base resins; conveying to a high-temperature reaction section to strip the wax layer, release the active load liquid and carry out interface grafting; through devolatilization, forming and curing, finished products are obtained. The application constructs a solid-state physical barrier shell through temperature control phase change coating technology, locks active substances in a low-temperature section to avoid early scorching and screw slipping, realizes interface limited release in a high-temperature section, constructs talcum powder composite cross-linking resin microsphere nodes, solves the problems of poor processing stability and many product crystal points, and realizes the balance of high-temperature creep resistance and high elongation at break.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, specifically to a cross-linking molding process for a high-toughness polyolefin composite leather material. Background Technology

[0002] Polyolefin thermoplastic elastomers are gradually replacing traditional polyvinyl chloride (PVC) materials in automotive interiors, furniture upholstery, and artificial leather due to their advantages such as low density, no plasticizer exudation, good weather resistance, and easy recycling. However, non-crosslinked polyolefin materials have poor heat creep resistance and are prone to dimensional collapse or deformation at high temperatures, making it difficult to meet the high-temperature performance requirements of automotive dashboards, door panels, and other components.

[0003] Silane grafting hydrolysis crosslinking technology is one of the main methods to improve the heat resistance and mechanical strength of polyolefin materials. In existing industrial production, a one-step process is used, in which liquid vinyl silane monomers and peroxide initiators are directly mixed with polyolefin resin, or directly injected into a twin-screw extruder via a liquid metering pump. This traditional direct addition method has process defects and performance bottlenecks in actual processing.

[0004] In terms of processing stability, liquid active additives come into direct contact with the resin matrix and the metal screw surface in the extruder's feeding and conveying sections. The lubricating effect of the liquid can easily cause screw slippage, leading to drastic fluctuations in extruder torque and current, resulting in unstable material delivery. Simultaneously, the shear heat generated by the extruder screw rotation can cause the peroxide initiator to partially decompose before the material is fully melted and plasticized, triggering early cross-linking reactions, i.e., scorching. This early, localized cross-linking forms a large number of unmeltable gel particles on the final leather material surface, damaging the product's appearance and smoothness.

[0005] In terms of material properties, traditional processes often aim for uniform dispersion of active substances in the matrix resin, with the goal of constructing a homogeneous, integral cross-linked network. While this dense, homogeneous network can improve the material's resistance to heat deformation, it also strongly restricts the movement of polymer chain segments, leading to an increase in the material's modulus and a decrease in its elongation at break and flexibility.

[0006] Therefore, this invention proposes a cross-linking molding process for high-toughness polyolefin composite leather materials to overcome the shortcomings of existing technologies. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a crosslinking molding process for high-toughness polyolefin composite leather materials. This process solves the problems of screw slippage and early scorching caused by premature release of active substances in traditional crosslinking processes, which leads to unstable processing and crystal point defects on the product surface. It also addresses the problem of excessive binding of molecular chains in homogeneous crosslinking networks, which prevents the material from simultaneously achieving high-temperature creep resistance and high elongation at break.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a crosslinking molding process for a high-toughness polyolefin composite leather material, comprising the following steps: Calcined talc powder is heated and sprayed with active load liquid while maintaining low-speed stirring. The active load liquid is then permeated by capillary force to obtain pre-impregnated talc powder. Pre-impregnated talc powder is heated, low-melting-point polyethylene wax is added and stirred at high speed to spread the molten low-melting-point polyethylene wax into a film, thus obtaining a hot coating material. The hot coating material was cooled and solidified to obtain phase change masterbatch; Phase change masterbatch and matrix resin were added to an extruder and subjected to solid conveying and plasticizing at low temperature to obtain a primary blended plasticized melt. The primary blended plasticized melt was transported to a high-temperature reaction section, where the wax layer was peeled off and the active loading liquid was released to carry out a grafting reaction, resulting in an interface-modified melt. High-toughness polyolefin composite leather material was obtained by devolatilization, molding and curing treatment of the interface-modified melt.

[0009] By adopting the above technical solution, and by constructing a spatiotemporally controllable interface-constrained reaction system using temperature-controlled phase change coating technology, the following beneficial effects and innovative mechanisms are obtained: This invention utilizes the synergistic effect of inorganic carrier adsorption and phase change material blocking to solve the problem of balancing processing stability and material mechanical properties.

[0010] In the preparation stage of pre-impregnated talc powder, the high oil absorption characteristics of the layered structure and micropores of calcined talc powder are utilized. Combined with low-speed stirring and heating to reduce liquid viscosity, the active loading liquid (silane and initiator) is drawn into the internal micro-regions of the calcined talc powder using capillary pressure difference. This process transforms the liquid chemically active substances into adsorbed substances within the solid powder body, avoiding slippage caused by the active liquid directly lubricating the screw.

[0011] In the preparation of hot-state coating materials and phase change masterbatches, a continuous and dense physical barrier shell is constructed on the surface of calcined talc powder adsorbed with active loading liquid, utilizing the phase change characteristics of low-melting-point polyethylene wax at a specific temperature. In the subsequent low-temperature solid conveying and preliminary plasticizing sections of the extruder, where the processing temperature is below or close to the phase change range of low-melting-point polyethylene wax and strong shear is lacking, this physical barrier shell maintains its structural integrity or a semi-solid, viscous, bound state. This isolation mechanism blocks the contact path between the initiator and the matrix resin in the low-temperature section, preventing ineffective decomposition and early grafting of dicumyl peroxide before reaching the reaction zone. This eliminates VOC volatilization at the feed port and crystal points generated by material scorching, ensuring stable mains current.

[0012] When the material enters the high-temperature reaction section of the extruder, the temperature jumps to a range with an extremely short initiator half-life. Combined with the action of the high-shear kneading element, the low-melting-point polyethylene wax shell undergoes a phase change melt and is forcibly peeled off. At this point, the active loading liquid, trapped within the micropores of the calcined talc powder, is released explosively. Because the active loading liquid diffuses from the interior of the inorganic filler outwards, its local concentration at the interface between the calcined talc powder and the polyolefin matrix is ​​much higher than at the far end of the matrix. According to free radical reaction kinetics, grafting and crosslinking reactions preferentially and concentrated within the micro-nano-scale interface layer on the talc powder surface.

[0013] The aforementioned interface-constrained reaction ultimately constructs a unique heterogeneous microstructure: an inorganic talc powder as a rigid core, encapsulating a hard resin shell with a high cross-linking density, dispersed within a relatively linear or slightly cross-linked flexible matrix continuous phase. These talc-based composite cross-linked resin microsphere nodes act as physical cross-linking points at high temperatures, restricting the macroscopic thermal creep of the molecular chains and endowing the material with excellent heat-resistant collapse resistance. Meanwhile, the flexible matrix continuous phase, occupying most of the volume, retains the original molecular chain flexibility and slippage ability of the polyolefin elastomer, giving the material a high elongation at break and a soft feel similar to natural leather.

[0014] Preferably, when the calcined talc powder is 100 parts by weight, the spray volume of the active load liquid is 10-15 parts by weight, the calcined talc powder is 1200-1300 mesh, the oil absorption value is 45-60 ml / 100g, the heating temperature is 70-75℃, the stirring speed is 400-600 rpm, and the time is 5-8 minutes.

[0015] By adopting the above technical solution, the mesh size and oil absorption value range of calcined talc powder are limited, ensuring that the inorganic carrier has sufficient specific surface area and pore volume to support the active load liquid and preventing liquid leakage caused by oversaturation. With the help of specific temperature and stirring parameters, it is ensured that the active load liquid can fully overcome surface tension and enter the micropores to achieve the maximum adsorption efficiency.

[0016] Preferably, the active loading solution is prepared by vinyltrimethoxysilane, dicumyl peroxide and antioxidant 1010 in a mass ratio of (14-16):1:(0.05-0.15).

[0017] By adopting the above technical solution, this specific component ratio balances the crosslinking rate and antioxidant protection while ensuring a sufficient grafting rate. The trace introduction of antioxidant 1010 protects the polypropylene backbone from degradation during the later stages of high-temperature processing without inhibiting the initiation of the crosslinking reaction, thus maintaining the long-term mechanical strength of the material.

[0018] Preferably, the amount of low-melting-point polyethylene wax added is 5-8 parts by weight, the melting point of the low-melting-point polyethylene wax is 85-90℃, the heating temperature is 95-105℃, the high-speed stirring speed is 1000-1500 rpm, and the time is 3-5 minutes.

[0019] By adopting the above technical solution, polyethylene wax with a specific melting point range is selected and matched with the sealing process temperature, ensuring that the wax has excellent flow and spreadability during the coating process, and can form a sealing film with uniform thickness and density; at the same time, the melting point range is slightly higher than the temperature of the extruder feeding section, ensuring the thermal stability of the sealing layer during the solid conveying stage.

[0020] Preferably, the cooling and curing is carried out in a cold mixer with cooling water, and the temperature after cooling is 35-40℃.

[0021] By adopting the above technical solution, rapid cooling treatment causes the polyethylene wax layer on the surface to crystallize quickly, which fixes the core-shell structure and prevents the phase change masterbatch from sticking and clumping during storage and transportation.

[0022] Preferably, the matrix resin is composed of polypropylene and ethylene-octene copolymer, wherein the polypropylene is 25-40 parts by weight and the ethylene-octene copolymer is 60-75 parts by weight.

[0023] By employing the above technical solution, ethylene-octene copolymer (POE) is used as the main flexible matrix, providing the material with an elastic feel; polypropylene (PP) serves as the heat-resistant reinforcing phase. The specific ratio of these two components, combined with interfacial crosslinking technology, allows the material to improve its temperature resistance through a crosslinked network while maximizing the toughening effect of POE.

[0024] Preferably, the amount of phase change masterbatch added is 20-30 parts by weight, and the amount of matrix resin added is 100 parts by weight.

[0025] By adopting the above technical solution, the addition ratio ensures that the molar concentration of the active crosslinking component in the system is within the optimal reaction window, which avoids both insufficient heat resistance caused by excessive crosslinking and difficulties in processing and molding and film breakage caused by excessive crosslinking.

[0026] Preferably, the temperature of the extruder feeding section and conveying section is controlled at 50-140℃, the temperature of the extruder plasticizing section is controlled at 160-175℃, and the temperature of the high-temperature reaction section is stepped up to 190-210℃.

[0027] By adopting the above technical solution, a temperature gradient field was established. The low-temperature section protects the integrity of the phase change sealing layer, achieving zero-leakage delivery of active materials; the medium-temperature section realizes resin melting and dispersion; and the high-temperature section utilizes thermal activation energy to instantly trigger initiator decomposition and wax layer peeling, achieving precise bursting of the chemical reaction at a specific spatial location.

[0028] Preferably, the curing treatment is carried out in a warm water or steam environment at 70-90℃ for 8-24 hours. By adopting the above technical solution, in a warm and humid environment, the silane groups grafted on the molecular chain undergo a full hydrolysis and condensation reaction, forming a final stable three-dimensional cross-linked network structure, thus solidifying the heat-resistant morphology of the material.

[0029] This invention provides a crosslinking molding process for a high-toughness polyolefin composite leather material. It offers the following advantages: 1. This invention utilizes the microporous physical adsorption of calcined talc powder combined with the phase change blocking effect of low-melting-point polyethylene wax to transform liquid active loading liquid into solid phase change masterbatch. In the feeding and conveying sections of the twin-screw extruder, the low-temperature environment maintains the low-melting-point polyethylene wax in a solid crystalline phase. The physical barrier shell completely cuts off the contact path between dicumyl peroxide and the matrix resin, avoiding early scorching caused by screw shear heat and screw slippage caused by liquid additives. This ensures stable mains current and eliminates the risk of film breakage during extrusion.

[0030] 2. This invention utilizes temperature step and shear control technology to achieve interfacial-confined release of active components, constructing a heterogeneous microstructure with talc as a rigid core, cross-linked resin as a hard shell, and linear polyolefin as a flexible continuous phase. This structure uses a hard interfacial layer to restrict the macroscopic thermal creep of molecular chains, reducing the amount of high-temperature thermal collapse deformation of the material; at the same time, it retains most of the linear molecular chain structure of the matrix resin, maintaining the original molecular chain flexibility and slippage ability of the ethylene-octene copolymer, making the high-toughness polyolefin composite leather material possess both excellent heat resistance, dimensional stability, and elongation at break.

[0031] 3. The adsorption-coupled phase change blocking process employed in this invention suppresses the escape of volatile silane monomers before high-temperature processing. By locking vinyltrimethoxysilane inside the inorganic carrier until it enters the fully enclosed high-temperature reaction section before release, the concentration of volatile organic compounds at the feed port is reduced, improving the working environment of the production workshop. Simultaneously, by avoiding gel particles generated by early local cross-linking, the surface of the high-toughness polyolefin composite leather material is ensured to be fine and uniform, free of crystal point defects, thus enhancing the product's appearance. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Examples 1-3: Example 1: This embodiment provides a cross-linking molding process for a high-toughness polyolefin composite leather material, specifically including the following steps: S1. 100 parts by weight of 1250 mesh calcined talc powder (oil absorption value 50 ml / 100 g) were put into a high-speed mixer with a heating jacket and heated to 72°C at 450 rpm. Then, 12.5 parts by weight of active loading liquid (prepared by vinyltrimethoxysilane, dicumyl peroxide, antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] in a mass ratio of 15:1:0.1) were sprayed onto the mixture and stirred at low speed at 72°C for 6 minutes. The active loading liquid was used to penetrate into the interlayer and micropores of the calcined talc powder by capillary force to obtain pre-impregnated talc powder. S2. Increase the speed of the mixer to 1200 rpm, and use shear heat and auxiliary heating to raise the temperature of the pre-impregnated talc powder to 100°C. Then add 6.5 parts by weight of low melting point polyethylene wax (melting point 88°C), and keep stirring at high speed at 100°C for 4 minutes to spread the molten low melting point polyethylene wax on the surface of the pre-impregnated talc powder agglomerates to form a film, thus obtaining the hot coating material. S3. The hot coating material is quickly discharged into a low-speed cold mixer with 5°C cooling water and cooled to 38°C at 150 rpm, so that the polyethylene wax layer on the surface crystallizes and solidifies, forming a structure with a solid physical barrier shell, and thus obtaining phase change masterbatch. S4. Mix 25 parts by weight of phase change masterbatch with 100 parts by weight of matrix resin (composed of 30 parts by weight of polypropylene and 70 parts by weight of ethylene-octene copolymer) evenly and then feed it into a twin-screw extruder. Solid conveying is carried out under the condition that the temperature of the extruder feeding section and conveying section is controlled at 100°C, and resin melting and filler dispersion are completed under the condition that the temperature of the extruder plasticizing section is controlled at 165°C. At this time, the polyethylene wax layer softens but the active components are still physically bound, and a primary blended plasticized melt is obtained. S5. The primary blended plasticized melt is transported to the high-temperature reaction section of the extruder. Under the high shear action of the temperature stepping to 200℃ and the presence of two sets of kneading blocks, the polyethylene wax layer is peeled off and the active load liquid is released instantly. The initiator preferentially initiates the grafting reaction at the talc interface, thus obtaining the interface-modified melt. S6. The interface-modified melt was devolatilized at -0.08MPa in the vacuum section of an extruder, and then subjected to T-die casting and curing in an 80℃ water bath for 12 hours to complete the final hydrolysis and crosslinking, resulting in a high-toughness polyolefin composite leather material.

[0034] Example 2: This embodiment provides a cross-linking molding process for a high-toughness polyolefin composite leather material, specifically including the following steps: S1. 100 parts by weight of calcined talc powder of 1300 mesh (oil absorption value 45ml / 100g) were put into a high-speed mixer and heated to 75°C at 600 rpm. 15 parts by weight of active loading liquid (prepared by vinyltrimethoxysilane, dicumyl peroxide and antioxidant 1010 in a mass ratio of 16:1:0.15) were sprayed on the mixture and stirred at 75°C for 5 minutes to obtain pre-impregnated talc powder. S2. Increase the mixer speed to 1500 rpm, heat the pre-impregnated talc powder to 105℃ (below the boiling point of the active load liquid), add 8 parts by weight of low melting point polyethylene wax (melting point 90℃), and stir at high speed for 3 minutes at 105℃ to ensure the formation of a thick-walled coating layer, thus obtaining the hot-state coating material. S3. The hot coated material is fed into a cold mixer and cooled to below 40°C to completely harden the outer wax film, thus obtaining phase change masterbatch. S4. Mix 30 parts by weight of phase change masterbatch with 100 parts by weight of matrix resin (composed of 40 parts by weight of polypropylene and 60 parts by weight of ethylene-octene copolymer) evenly and then feed it into a twin-screw extruder. Solid conveying is carried out under the condition that the temperature of the extruder feeding section and conveying section is controlled at 140°C, and resin melting and filler dispersion are completed under the condition that the temperature of the extruder plasticizing section is controlled at 175°C. At this time, the polyethylene wax layer softens but the active components are still physically bound, and a primary blended plasticized melt is obtained. S5. The primary blended plasticized melt is transported to the reaction section of the extruder. Under high temperature and strong shear conditions of 210°C, the thickened waxy blocking layer is forcibly peeled off and the interfacial cross-linking reaction is triggered to obtain the interfacial modified melt. S6. The interface-modified melt was subjected to vacuum devolatilization, mold forming, and steam curing at 90°C for 24 hours to obtain a high-toughness polyolefin composite leather material.

[0035] Example 3: This embodiment provides a cross-linking molding process for a high-toughness polyolefin composite leather material, specifically including the following steps: S1. 100 parts by weight of calcined talc powder of 1200 mesh (oil absorption value 60ml / 100g) were put into a high-speed mixer and heated to 70°C at 400rpm. 10 parts by weight of active loading liquid (prepared by vinyltrimethoxysilane, dicumyl peroxide, and antioxidant 1010 in a mass ratio of 14:1:0.05) were sprayed on the mixture and stirred at 70°C for 8 minutes to obtain pre-impregnated talc powder. S2. Increase the speed of the mixer to 1000 rpm, heat the pre-impregnated talc powder to 95°C, add 5 parts by weight of low melting point polyethylene wax (melting point 85°C), and stir at 95°C for 5 minutes to form a thin coating, thus obtaining the hot-state coating material. S3. The hot coated material is fed into a cold mixer and cooled to 35°C to obtain phase change masterbatch; S4. Mix 20 parts by weight of phase change masterbatch with 100 parts by weight of matrix resin (composed of 25 parts by weight of polypropylene and 75 parts by weight of ethylene-octene copolymer) evenly and then add it to a twin-screw extruder. Solid conveying is carried out under the condition that the temperature of the extruder feeding section and conveying section is controlled at 50°C, and resin melting and filler dispersion are completed under the condition that the temperature of the extruder plasticizing section is controlled at 160°C. At this time, the polyethylene wax layer softens but the active components are still physically bound, and a primary blended plasticized melt is obtained. S5. The primary blended plasticized melt is transported to the reaction section of the extruder, where a thin wax film is peeled off and active substances are released at a temperature of 190°C. Moderate interfacial crosslinking is completed under a low thermal history, resulting in an interfacial modified melt. S6. The interface-modified melt was subjected to vacuum devolatilization, casting molding, and curing in 70°C warm water for 8 hours to obtain a high-toughness polyolefin composite leather material.

[0036] Comparative Examples 1-3: Comparative Example 1: Compared with Example 1, the difference lies in omitting the masterbatch preparation process in steps S1 to S3 and adjusting the feeding method in step S4. The specific operation is as follows: In step S4, 21.0 parts by weight of calcined talc powder, 1.4 parts by weight of low-melting-point polyethylene wax, and 100 parts by weight of matrix resin (30 parts by weight of polypropylene and 70 parts by weight of ethylene-octene copolymer) are mixed evenly and then added to the main feed port of a twin-screw extruder. Simultaneously, 2.6 parts by weight of active loading liquid (with the same ratio as in Example 1) is directly injected into the barrel of the first conveying section of the extruder using a high-pressure liquid metering pump. All other process parameters (temperature setting, screw combination, post-treatment, etc.) are the same as in Example 1.

[0037] Comparative Example 2: Compared to Example 1, the difference lies in the omission of the phase change blocking process in step S2, and the timing of the addition of the phase change blocking agent is changed. Specifically, the operation is as follows: After obtaining the pre-impregnated talc powder in step S1, the heating and addition of polyethylene wax are not performed; instead, step S3 is directly executed for cooling. The 6.5 parts by weight of low-melting-point polyethylene wax originally planned to be added in step S2 is instead used as an external lubricant in step S4, and is directly added to the extruder along with the modified filler masterbatch and the matrix resin. Everything else is the same as in Example 1.

[0038] Comparative Example 3: Compared to Example 1, the difference lies in reversing the preparation order of steps S1 and S2, resulting in the failure to form a core-shell structure coating the active liquid. The specific operation is as follows: First, 100 parts by weight of calcined talc powder and 6.5 parts by weight of low-melting-point polyethylene wax are mixed at high speed at 100°C to pre-coat the surface of the talc powder with a wax layer. After cooling to 72°C, 12.5 parts by weight of active load liquid are sprayed and mixed to allow the active load liquid to adhere to the outer surface of the wax layer and the uncoated areas. The subsequent extrusion process steps S4 to S6 are the same as in Example 1.

[0039] Test Example 1-2: Test Example 1: To verify the stability, safety, and control over product appearance quality of the crosslinking molding process proposed in this application in continuous industrial production, the intermediate materials and final high-toughness polyolefin composite leather materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were selected for the following tests: Main motor current fluctuation rate test: Start the twin-screw extruder, and after the temperature reaches the set process parameters and runs stably for 30 minutes, begin recording the current value of the main motor of the extruder. Record continuously for 120 minutes, sampling once every 5 minutes. Calculate the current fluctuation rate using the formula: (maximum current value - minimum current value) / average current value × 100%. The main motor current fluctuation rate reflects the stability of material conveying and the uniformity of plasticization within the screw. Excessively high fluctuation rate indicates sudden torque changes caused by feed slippage or localized cross-linking (scorching).

[0040] Volatile Organic Compounds (VOCs) Concentration Monitoring at the Feed Port: A handheld photoionization detector (PID) was used, with the probe positioned 10 cm above the main feed port of the twin-screw extruder. During stable extruder operation, the total VOCs concentration (in ppm) generated by the volatilization of vinyltrimethoxysilane and dicumyl peroxide was continuously monitored and recorded. This indicator characterizes the physical blocking efficiency of the active loading fluid and the safety of the processing.

[0041] Statistical analysis of crystal point defects: Five 1-meter-long samples (with a fixed width of 1.2 meters) were randomly cut from high-toughness polyolefin composite leather sheets produced continuously in each experimental group. Under a standard light source, the number of unmelted gel particles with a diameter greater than 0.5 mm per square meter was manually counted. The average value of the five samples was taken as the final result. The number of crystal points directly reflects whether early pre-crosslinking exists in the extruder feeding and plasticizing sections.

[0042] The test results are as follows: Table 1. Summary of Process Stability and Surface Quality Test Data Example 1 1.2 4.3 0 It runs smoothly and has no odor. Example 2 2.1 8.7 1.2 Occasionally, extremely small crystal points are observed. Example 3 0.9 5.1 0 Stable operation Comparative Example 1 18.4 158.2 64.5 Feed backflow from the feed inlet, with a strong pungent odor. Comparative Example 2 6.8 89.4 23.8 There is a distinct odor Comparative Example 3 3.5 112.6 41.2 The current is relatively stable, but there are many crystal points. As shown in Table 1, Comparative Example 1, using the traditional direct liquid injection process, exhibited a main unit current fluctuation rate as high as 18.4%, and a VOCs concentration at the feeding port reaching 158.2 ppm, resulting in severe crystal point defects on the product surface. This is because liquid vinyltrimethoxysilane directly contacts the high-temperature screw and resin, causing volatilization and early grafting reactions in the feeding section. The volatilized silane gas accumulates at the feeding port, creating a safety hazard. Simultaneously, the liquid additives act as an unstable external lubricant, leading to screw slippage and causing drastic torque fluctuations. The cross-linked gel generated in the early reaction cannot melt in subsequent stages, ultimately forming numerous crystal points on the leather surface.

[0043] Comparative Example 2 used talc for adsorption, but no phase change blocking agent was introduced. Data showed that the VOC concentration in Comparative Example 2 remained at a high level (89.4 ppm), and a certain number of crystal points were present (23.8 per m³). 2 This indicates that simple physical adsorption cannot completely resist the thermal history and negative pressure suction effect of the extruder feeding section. Some of the active load liquid is released prematurely before the resin melts, resulting in local scorching.

[0044] Comparative Example 3 altered the preparation sequence, first coating with a wax layer and then spraying with the active liquid, resulting in the active loading liquid being located on the outermost layer of the composite particles. Although the polyethylene wax layer provided some lubrication, reducing the current fluctuation rate compared to Comparative Example 1 (3.5%), the active material was directly exposed, preventing delayed release. VOCs concentration (112.6 ppm) and the number of crystal points (41.2 / m²) remained relatively high. 2 The level remains high and cannot meet the requirements for appearance quality.

[0045] In contrast, the main unit current fluctuation rate in Examples 1 to 3 was controlled below 2.5%, the VOCs concentration at the feed port was below 10 ppm, and the apparent crystal points were close to or equal to zero. This indicates that the adsorption-coupled phase change blocking technology route is effective. In the low-temperature environment of the extruder feeding and conveying section, the solid physical barrier shell formed by the low-melting-point polyethylene wax tightly seals vinyltrimethoxysilane and dicumyl peroxide within the micro-regions of calcined talc, completely blocking the early contact path between the active material and the matrix resin, while also preventing volatilization. Only when the material enters the high-temperature, high-shear zone does the phase change blocking layer melt and peel off, releasing the active material. This precise control over the time and space of the chemical reaction ensures the stability of the processing and the high homogeneity of the final product.

[0046] Test Example 2: To verify the effect of the crosslinking molding process proposed in this application on the final physical and mechanical properties and temperature resistance of the material, especially to verify the contribution of the interface delayed crosslinking structure to the rigid-flexible balance characteristics, high-toughness polyolefin composite leather material sheets prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were selected for sample preparation and testing.

[0047] The specific testing standards and methods are as follows: Tensile property testing (tensile strength and elongation at break): Following ASTM D412 standard, high-toughness polyolefin composite leather sheets were cut into dumbbell-shaped specimens. Testing was conducted using a universal testing machine at a tensile speed of 500 mm / min. The maximum stress at specimen fracture was recorded as the tensile strength (MPa), and the ratio of the increment in gauge distance at fracture to the initial gauge length was recorded as the elongation at break (%). Elongation at break is a core indicator characterizing the toughness of a material.

[0048] Shore hardness test: According to ASTM D2240 standard, multiple layers of high-toughness polyolefin composite leather material sheets are stacked to a thickness greater than 6 mm. A Shore A hardness tester is vertically pressed into the sample surface, and the stable value is read after 15 seconds. This index characterizes the softness of the leather material to the touch.

[0049] Gel content test (crosslinking degree characterization): Xylene extraction method was used according to ASTM D2765 standard. A certain mass of ( The chopped sample was refluxed in boiling xylene for 12 hours, dried, and the mass of the residual insoluble matter was measured. The calculation formula is: ; The gel content reflects the degree of construction of the chemical cross-linking network within the system.

[0050] High-Temperature Thermal Slump Deformation Test: Based on the general testing standards for automotive interior materials, a strip measuring 150 mm in length and 25 mm in width was cut. One end of the strip was horizontally fixed to a bracket, with a 100 mm overhang. The bracket and the strip were placed in a 120°C hot air circulating oven for 1 hour. The vertical sag distance (in millimeters) of the overhanging end of the strip after heating was measured. A smaller value indicates better dimensional stability of the material at high temperatures, i.e., higher heat creep resistance.

[0051] The test results are as follows: Table 2. Summary of Mechanical and Heat Resistance Test Data Example 1 16.4 623 82 44.5 2.5 Example 2 19.8 455 88 56.2 1.2 Example 3 12.5 742 76 32.8 5.8 Comparative Example 1 9.2 185 81 18.4 14.6 Comparative Example 2 11.7 240 83 24.1 10.3 Comparative Example 3 15.8 312 84 43.9 2.8 As shown in Table 2, the properties of Comparative Examples 1 and 2 are all lower than those of the Example. The data shows that the gel content of Comparative Examples 1 and 2 is only 18.4% and 24.1%, respectively, and the thermal collapse deformation exceeds 10 mm, indicating extremely poor heat resistance. This is because, in the absence of effective phase change blocking, vinyltrimethoxysilane volatilizes significantly at the front end of the extruder, resulting in a severely insufficient concentration of crosslinking agent actually participating in the grafting reaction, making it impossible to construct an effective three-dimensional heat-resistant network. Simultaneously, the defects caused by early localized scorching become stress concentration points during the stretching process, leading to a decrease in tensile strength and elongation at break.

[0052] The data from Comparative Example 3 are of significant comparative value. The gel content of Comparative Example 3 (43.9%) is very close to that of Example 1 (44.5%), and its thermal collapse deformation (2.8 mm) is also comparable to that of Example 1 (2.5 mm), indicating that Comparative Example 3 has indeed achieved chemical cross-linking and possesses temperature resistance. However, the elongation at break of Comparative Example 3 is only 312%, far lower than the 623% of Example 1. This difference confirms the crucial role of the interface-constrained reaction mechanism of this invention: In Comparative Example 3, due to the incorrect sequence of wax coating followed by liquid spraying, the active material was located on the outermost layer and rapidly dispersed upon entering the extruder, undergoing a homogeneous reaction with the matrix resin. This resulted in the entire continuous phase of the polyolefin elastomer (POE) being bound by the cross-linked network, restricting the movement of molecular chain segments, causing the material to become hard and brittle overall, and losing the high ductility expected of an elastomer.

[0053] Example 1 employed a specific process of adsorption followed by blocking, locking the active material within the talc carrier and releasing it only during the high-temperature shearing phase. Controlled by reaction kinetics, the cross-linking grafting reaction preferentially occurred at the interface between the talc filler and the resin, forming numerous rigid talc composite cross-linked resin microsphere nodes, while the matrix resin, far from the filler, maintained a relatively linear molecular structure. This heterogeneous structure endowed the material with a unique mechanical response mechanism: under heat, the rigid interface layer provided skeletal support; under tensile stress, the uncross-linked linear matrix provided space for molecular chain slippage and orientation.

[0054] In summary, Examples 1 to 3 successfully resolved the contradiction between heat resistance and high toughness in traditional crosslinking processes through temperature-controlled phase change coating technology. While ensuring excellent high-temperature creep resistance (low thermal collapse) of the material, they retained high elongation at break and a soft feel similar to natural leather. Example 1, in particular, achieved the optimal balance of performance with a moderate gel content, verifying the advanced nature of the present invention.

Claims

1. A cross-linking molding process for a high-toughness polyolefin composite leather material, characterized in that, Includes the following steps: Calcined talc powder is heated and sprayed with an active load liquid while maintaining low-speed stirring. The active load liquid is then permeated by capillary force to obtain pre-impregnated talc powder. The active loading solution is prepared by mixing vinyltrimethoxysilane, dicumyl peroxide and antioxidant 1010 in a mass ratio of (14-16):1:(0.05-0.15); The pre-impregnated talc powder is heated, low-melting-point polyethylene wax is added and stirred at high speed to spread the molten low-melting-point polyethylene wax into a film, thus obtaining a hot-state coating material. The hot coating material was cooled and solidified to obtain phase change masterbatch; The phase change masterbatch and the matrix resin were added to an extruder and subjected to solid conveying and plasticizing at low temperature to obtain a primary blended plasticized melt. The primary blended plasticized melt is transported to a high-temperature reaction section to peel off the wax layer and release the active loading liquid for grafting reaction, thereby obtaining an interface-modified melt. The interface-modified melt is subjected to devolatilization, molding, and curing treatment to obtain a high-toughness polyolefin composite leather material.

2. The cross-linking molding process for a high-toughness polyolefin composite leather material according to claim 1, characterized in that, When the calcined talc powder is 100 parts by weight, the spray volume of the active loading liquid is 10-15 parts by weight, the calcined talc powder is 1200-1300 mesh, the heating temperature is 70-75℃, the low-speed stirring speed is 400-600 rpm, and the time is 5-8 minutes.

3. The cross-linking molding process for a high-toughness polyolefin composite leather material according to claim 1, characterized in that, When the calcined talc powder is 100 parts by weight, the amount of low-melting-point polyethylene wax added is 5-8 parts by weight, the heating temperature is 95-105℃, the high-speed stirring speed is 1000-1500 rpm, and the time is 3-5 minutes.

4. The cross-linking molding process for a high-toughness polyolefin composite leather material according to claim 1, characterized in that, The cooling and curing process is carried out in a cold mixer supplied with cooling water, and the temperature after cooling is 35-40℃.

5. The cross-linking molding process for a high-toughness polyolefin composite leather material according to claim 1, characterized in that, The matrix resin is composed of polypropylene and ethylene-octene copolymer, wherein the polypropylene comprises 25-40 parts by weight and the ethylene-octene copolymer comprises 60-75 parts by weight.

6. The cross-linking molding process for a high-toughness polyolefin composite leather material according to claim 1, characterized in that, When the matrix resin is 100 parts by weight, the amount of phase change masterbatch added is 20-30 parts by weight.

7. The cross-linking molding process for a high-toughness polyolefin composite leather material according to claim 1, characterized in that, The temperature of the extruder feeding section and conveying section is controlled at 50-140℃, and the temperature of the extruder plasticizing section is controlled at 160-175℃.

8. The cross-linking molding process for a high-toughness polyolefin composite leather material according to claim 1, characterized in that, The temperature of the high-temperature reaction section jumps to 190-210℃.

9. The cross-linking molding process for a high-toughness polyolefin composite leather material according to claim 1, characterized in that, The conditioning treatment involves processing in a warm water or steam environment at 70-90℃ for 8-24 hours.