Lightweight high-resilience automobile door and window frame microcellular foamed sealing material

Abstract

The application relates to the field of polymer material batching and processing, and discloses a lightweight high-resilience automobile door and window frame microcellular foaming sealing material, which is prepared from a ternary ethylene-propylene-diene rubber as a base body, zinc diacrylate, polyethylene glycol and a foaming agent and the like. The application utilizes polymer ion clusters generated in situ from zinc diacrylate and covalent bonds to construct a double-crosslinking network, improves the melt strength in the foaming stage, prevents bubble hole collapse and endows the material with high resilience; meanwhile, the early-stage agglomeration and scorching of the polar monomer are inhibited by virtue of the coordination shielding effect of the polyethylene glycol, in the extrusion molding stage of the preparation process, an inverse ladder temperature control strategy with the die temperature being lower than the metering section temperature is adopted, so that the ion clusters are associated at the moment of material ejection to establish the initial strength of the surface layer, thereby resisting the internal pressure of vulcanization foaming and inhibiting thermal back rolling shrinkage, and the unification of low density, high resilience and dimensional stability of the sealing material is realized.

Description

Technical Field

[0001] This invention relates to the field of polymer material formulation and processing, specifically to a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames. Background Technology

[0002] Ethylene propylene diene monomer (EPDM) rubber possesses a stable main chain structure and excellent weather resistance, making it a fundamental material for manufacturing automotive door and window frame sealing strips. In response to the overall lightweighting trend in the automotive industry, reducing the apparent density of sealing materials through microporous foaming technology has become a key area of ​​technological advancement in this field.

[0003] In the pursuit of lower density foaming, the amount of gas generated within the system increases significantly. When the gas expands violently within the viscous rubber matrix, the conventional single covalent cross-linked network is usually insufficient to provide enough melt tensile strength to support the thinning and elongation of the cell walls in the early stages of foaming. This mismatch between the melt viscoelasticity and the gas expansion stress causes the cell walls to rupture, merge, or even collapse due to the inability to withstand the internal pressure. The damage to the microstructure directly leads to a decrease in the stress buffering capacity of the foamed material on a macroscopic scale, manifested as a decrease in resilience and an increase in compression set, failing to meet the sealing and sound insulation requirements of automotive doors and windows under long-term, high-frequency opening and closing conditions.

[0004] To improve melt strength during the foaming process, existing processes attempt to introduce polar reinforcing monomers or metal salts into the formulation. However, EPDM rubber is inherently a non-polar polymer, and the compatibility of polar components in the matrix is ​​inherently insufficient. Under the high temperature and strong shear of the internal mixing process, these polar substances are prone to local agglomeration and premature free radical reactions, leading to early scorching of the rubber compound. This not only significantly narrows the safe processing window for continuous production but also results in uneven distribution of nucleation points, leading to a coarse cell structure of varying sizes in the final product.

[0005] Furthermore, automotive sealing strips are typically formed using a continuous extrusion process combined with atmospheric pressure hot air vulcanization. When the material, at its high temperature, leaves the extruder die, the internal chemical cross-linking is not yet fully established, and the melt lacks sufficient initial surface strength. Once it enters the atmospheric pressure vulcanization environment, the concentrated decomposition of the internal foaming agent generates enormous internal expansion pressure. The release of thermal stress and the lack of shrinkage resistance intertwine, easily triggering thermal rewinding and shrinkage of the extruded preform. This dimensional uncontrollability makes it difficult for door and window sealing strips with complex cross-sectional shapes to maintain their designed geometric contours, accompanied by surface collapse defects, affecting the stable mass production of high-quality, lightweight sealing materials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames. It solves the problems of cell collapse and reduced resilience caused by insufficient melt strength during the low-density process of existing EPDM rubber foam materials, early scorching and rough cells caused by poor compatibility of polar reinforcing components, and thermal rewinding shrinkage and dimensional instability caused by insufficient surface strength during continuous extrusion.

[0007] To achieve the above objectives, the first aspect provides a lightweight, high-resilience microporous foam sealing material for automotive door and window frames, the raw material system comprising, by weight: EPDM rubber: 100 parts; carbon black: 40.0–60.0 parts; paraffin oil: 40.0–70.0 parts; zinc oxide: 1.0–2.0 parts; stearic acid: 1.0 part; polyethylene glycol: 0.5–2.0 parts; zinc stearate: 1.5–3.0 parts; zinc diacrylate: 3.0–8.0 parts; dicomir peroxide: 1.5–2.5 parts; scorching inhibitor CTP: 0.2–0.5 parts; 4,4'-oxobisbenzenesulfonyl hydrazine: 2.0–4.0 parts.

[0008] By employing the above technical solution, this invention utilizes the in-situ reaction of zinc diacrylate and di-coumer peroxide during the vulcanization process. The resulting long-chain segments of polyzinc diacrylate exhibit strong electrostatic attraction between the carboxyl groups on their side groups and zinc ions in the system. These segments aggregate and self-assemble into ion clusters with physical cross-linking properties in the non-polar rubber phase. These ion clusters interpenetrate and entangle with the carbon-carbon covalent cross-linking points initiated by the peroxide. Furthermore, during the dynamic process of foaming gas expansion, the ion clusters can dissipate stress through the dissociation and recombination of physical association, endowing the viscous melt with the necessary interfacial tensile strength, thereby microscopically locking in the foaming gas and preventing cell coalescence or rupture. Simultaneously, the ether oxygen atoms on the polyethylene glycol molecular chain can form spatial coordination with the zinc ions in the zinc diacrylate. This coordination shielding effect effectively reduces the early reactivity of polar monomers during the shearing stages of mixing and extrusion. Combined with the regulation of free radical capture by the anti-scorching agent CTP, this jointly solves the problem of early agglomeration and scorching of polar monomers, ensuring the flow stability of the compound during processing. In addition, zinc stearate plays a role in regulating interfacial tension in the system. By reducing the nucleation work between the foaming agent 4,4'-oxobisbenzenesulfonylhydrazine and the matrix, it induces a large number of fine heterogeneous nucleation sites in conjunction with the polar micro-regions formed by ion clusters. This is the structural basis for achieving both low density and high resilience.

[0009] Preferably, the ethylene propylene diene monomer (EPDM) rubber contains 55wt% to 70wt% of repeating ethylene units, 4wt% to 9wt% of repeating diene monomer (ENB), and has a Mooney viscosity (ML(1+4)) at 125°C of 60 to 80; the polyethylene glycol has a weight-average molecular weight of 4000 to 6000 and a hydroxyl value of 18 mgKOH / g to 28 mgKOH / g.

[0010] The selection of a substrate with specific ethylene content and Mooney viscosity is to balance the strength and flowability of the raw rubber, while the high molecular weight of polyethylene glycol ensures effective spatial interference of the ionic bonding process, thereby expanding the processing window.

[0011] A second aspect of this invention provides a method for preparing a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames, comprising the following steps:

[0012] S1, First stage of internal mixing: EPDM rubber, carbon black, paraffin oil, zinc oxide, stearic acid, polyethylene glycol and zinc stearate are put into an internal mixer and mixed. After the rubber is discharged, it is naturally cooled to obtain the first stage of masterbatch.

[0013] S2, Two-stage mixing: The first stage masterbatch is put into the open mill, and zinc diacrylate, dicomir peroxide, anti-scorching agent CTP and 4,4'-oxobisbenzenesulfonyl hydrazine are added in sequence for mixing. The mixed rubber is then discharged to obtain the finished product.

[0014] S3. Extrusion molding: The compound rubber product is fed into a single screw extruder and extruded. The temperature is controlled in reverse stepwise. The die head temperature is set to be 10℃~20℃ lower than the metering section temperature of the extruder to obtain the extruded preform.

[0015] S4. Foaming and vulcanization: The extruded preform is fed into a normal pressure hot air vulcanization tunnel for foaming and vulcanization. Finally, it is cooled to room temperature to obtain the foamed sealing material.

[0016] In the preparation process, zinc diacrylate is introduced in a lower-temperature open mill environment in step S2 to avoid the high-temperature zone that may occur during internal mixing, preventing premature self-polymerization of polar monomers and resulting in uneven dispersion. For the extrusion molding stage, this invention achieves instantaneous locking of the melt's physical state through a reverse-step temperature control strategy in step S3. When the compound is in the metering section of the extruder, the higher temperature causes the physical ionic bonds to be in a thermally dissociated state, ensuring low melt viscosity and good flowability. When the material reaches the die, the temperature drops sharply, rapidly enhancing the physical association of the zinc diacrylate ion clusters, thus producing a strengthening effect. This surface strength established at the moment of demolding effectively resists the internal pressure generated by intense foaming in the subsequent vulcanization tunnel, preventing the escape of expanding gas and overcoming the rollback shrinkage caused by thermal stress release by enhancing melt resilience.

[0017] Preferably, in step S3, the temperature of the extruder in zones 1-2 is set to 85℃-100℃, the temperature of zones 3-4 is set to 120℃-135℃, the temperature of zone 5 (i.e., the metering section) is set to 145℃-155℃, and the temperature of the die head is set to 130℃-140℃.

[0018] This temperature gradient setting ensures that the chemical crosslinking kinetics and physical association equilibrium within the system are in a coordinated state throughout the entire process from solid transport and plasticization to final molding.

[0019] Furthermore, the apparent density of the final prepared material was 0.463 g / cm³. 3 ~0.506g / cm 3 The percentage of the actual gel content of the rubber matrix in the extracted residue was 88.4% to 91.5%.

[0020] This invention provides a lightweight, high-resilience microporous foam sealing material for automotive door and window frames. It offers the following advantages:

[0021] 1. This invention introduces a specific proportion of zinc diacrylate into the EPDM rubber formulation, thereby constructing an ion cluster structure with physical cross-linking properties in situ on the basis of a conventional vulcanization network. This double cross-linking network provides higher melt viscoelasticity during the foaming expansion stage, which can effectively support the extremely thinning extension of the cell walls without cracking or collapsing, thereby achieving a combination of low density and high resilience performance, so that the material has excellent compression recovery force while maintaining lightweight.

[0022] 2. This invention utilizes a stepped temperature control strategy where the die temperature is lower than the metering section temperature during extrusion molding, achieving instantaneous regulation of the material's microscopic physical state. When the rubber compound leaves the die, the temperature drop triggers the rapid association of zinc diacrylate ion clusters, thereby imparting the necessary initial surface strength to the melt before foaming. This effectively locks in expanding gas and resists internal pressure, thus ensuring the dimensional stability and cross-sectional regularity of the microporous sealing strip.

[0023] 3. This invention solves the processing problem of easy agglomeration and early scorching of polar metal salts in non-polar rubber matrices by synergistic combination of polyethylene glycol, zinc stearate and anti-scorching agent CTP. The spatial coordination of polyethylene glycol and zinc ions effectively shields the early reactivity of zinc diacrylate, while zinc stearate induces the foaming agent to achieve uniform heterogeneous nucleation by adjusting the interfacial tension, thereby widening the production and processing window and ensuring that the bubbles can form a fine and uniform distribution structure in the matrix, fundamentally improving the surface quality and mechanical property consistency of the finished product. Attached Figure Description

[0024] Figure 1Figure 1 shows a comparison of the Mooney scorch performance of the various groups of rubber compounds of the present invention. Figure 2 shows a comparison of the lowest Mooney viscosity of the various groups of rubber compounds, and Figure 3 shows a comparison of the scorch times t5 and t35 of the various groups of rubber compounds.

[0025] Figure 2 This is a trend chart showing the gel content distribution of the foamed sealing materials in each group of the present invention;

[0026] Figure 3 This is a comparison chart of the apparent density test results of the microporous foamed sealing materials of different groups in this invention;

[0027] Figure 4 Figure 1 shows a line graph comparing the long-term compression set performance of various embodiments and comparative examples of the present invention. Figure 2 shows a schematic diagram of the compression set test results at room temperature (23°C) and Figure 3 shows a schematic diagram of the compression set test results at high temperature (70°C).

[0028] Figure 5 Figure 1 shows a comparison of the mechanical strength and tear resistance of various embodiments and comparative examples of the present invention. Figure 2 shows a comparison of the tensile strength of the materials in each group, Figure 3 shows a comparison of the elongation at break of the materials in each group, and Figure 4 shows a comparison of the tear strength of the materials in each group.

[0029] Figure 6 Line graphs showing the test results of heat shrinkage rates for various embodiments and comparative examples of the present invention;

[0030] Figure 7 This is a schematic diagram showing the static water absorption rate distribution characteristics of the microporous foamed sealing materials of each group in this invention. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0032] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0033] Ethylene propylene diene monomer (EPDM) rubber, CAS number 25038-36-2, contains 55wt%–70wt% ethylene repeating units, 4wt%–9wt% diene monomer ENB repeating units, Mooney viscosity ML(1+4)@125℃ is 60–80, molecular weight distribution index is 2.5–4.5, and density is 0.86 g / cm³. 3~0.87g / cm 3 It has a crystallinity of 10% to 20% and a secondary transition point (glass transition temperature) of -55℃ to -45℃.

[0034] Zinc diacrylate (ZDA), CAS number 14643-87-9, molecular formula C6H6O4Zn, purity greater than or equal to 98%, appearance is white powder, median diameter D50 is 5μm~15μm.

[0035] Polyethylene glycol (PEG), CAS number 25322-68-3, weight-average molecular weight 4000–6000, hydroxyl value 18 mg KOH / g–28 mg KOH / g, crystallinity ≥80%, density 1.15 g / cm³ 3 ~1.25g / cm 3 .

[0036] Zinc stearate (ZnSt), CAS number 557-05-1, has a free acid content of less than or equal to 1.0%, a zinc oxide content of 12.5wt% to 14wt%, and a melting point of 118℃ to 125℃.

[0037] 4,4'-Oxobis(benzenesulfonylhydrazine) (OBSH), CAS No. 80-51-3, molecular formula C 12 H 14 N4O5S2 has a decomposition temperature of 155℃~165℃, a gas emission rate of 120ml / g~130ml / g, and an average particle size of 5μm~10μm.

[0038] The scorching inhibitor CTP, CAS number 17796-82-6, chemical name N-cyclohexylthiophthalimide, has a purity greater than or equal to 98%.

[0039] Dicomir peroxide (DCP, CAS No. 80-43-3), zinc oxide (ZnO, CAS No. 1314-13-2), stearic acid (SA, CAS No. 57-11-4), carbon black (CAS No. 1333-86-4), and paraffin oil (CAS No. 8012-95-1) are all commercially available grades commonly used in the rubber industry.

[0040] Example 1:

[0041] This embodiment provides a method for preparing a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames, including the following steps:

[0042] (1) A period of secret refining:

[0043] Weigh out 100 parts EPDM, 50.0 parts carbon black, 55.0 parts paraffin oil, 1.5 parts zinc oxide, 1.0 part stearic acid, 1.0 part polyethylene glycol (weight average molecular weight 4000), and 1.5 parts zinc stearate by weight. Add the above raw materials to an internal mixer, setting the initial speed to 40-45 rpm and the initial temperature to 50°C. When the material heats up to 110-115°C under shear heat, maintain the mixing for 2-3 minutes, then discharge the binder and allow it to cool naturally to 30-40°C to obtain a first-stage masterbatch.

[0044] (2) Two-stage mixing:

[0045] A section of masterbatch is fed into a two-roll mill, with the roll temperature controlled at 45℃~55℃ and the roll gap adjusted to 2mm~4mm. Then, 5.0 parts of zinc diacrylate, 2.0 parts of DCP, 0.3 parts of CTP (anti-scorching agent), and 3.0 parts of OBSH are added sequentially. First, the material is fed into the rolls, and after feeding is complete, it is cut 3 to 5 times on each side to ensure uniform dispersion of zinc diacrylate within the polar micro-regions established by the masterbatch. Then, the mixture is discharged, with the discharge temperature controlled at 85℃~90℃, yielding the finished compound.

[0046] (3) Extrusion molding:

[0047] The compounded rubber was fed into a single-screw extruder with a length-to-diameter ratio of 16. The temperatures for zones 1 and 2 were set to 90℃–95℃, zones 3 and 4 to 125℃–130℃, and zone 5 to 150℃. A reverse stepped temperature control was then implemented, setting the die temperature to 135℃.

[0048] (4) Foaming vulcanization:

[0049] The extruded preform enters a three-stage atmospheric pressure hot air vulcanization tunnel, with the temperature zones of each stage set at 185℃, 210℃, and 215℃ respectively. The total residence time of the material in the tunnel is 300s to 360s, and the residence time in each temperature zone is the same. Finally, it is naturally cooled to room temperature to obtain a microporous foamed sealing material.

[0050] Example 2:

[0051] This embodiment provides a method for preparing a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames, including the following steps:

[0052] (1) A period of secret refining:

[0053] Weigh out 100 parts EPDM, 40.0 parts carbon black, 70.0 parts paraffin oil, 1.2 parts zinc oxide, 1.0 part stearic acid, 2.0 parts polyethylene glycol (weight average molecular weight 6000), and 3.0 parts zinc stearate. The mixing process is the same as in Example 1, and the discharge temperature is controlled at 110℃.

[0054] (2) Two-stage mixing:

[0055] Add 3.0 parts zinc diacrylate, 1.5 parts DCP, 0.5 parts CTP (anti-scorching agent), and 4.0 parts OBSH to a first-stage masterbatch. The mixing process is the same as in Example 1, and the discharge temperature is controlled at 80℃~85℃.

[0056] (3) Extrusion molding:

[0057] The extruder temperature is set at 85℃~90℃ for zones 1 and 2, 120℃~125℃ for zones 3 and 4, 145℃ for zone 5, and 135℃ for the die head.

[0058] (4) Foaming vulcanization:

[0059] The temperature zones of the sulfidation tunnel were set at 180℃, 200℃, and 210℃, with a dwell time of 360s to 390s. The dwell time was the same for each temperature zone. Finally, the material was naturally cooled to room temperature to obtain a microporous foamed sealing material.

[0060] Example 3:

[0061] This embodiment provides a method for preparing a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames, including the following steps:

[0062] (1) A period of secret refining:

[0063] Weigh out 100 parts EPDM, 60.0 parts carbon black, 40.0 parts paraffin oil, 1.6 parts zinc oxide, 1.0 part stearic acid, 0.5 parts polyethylene glycol (weight average molecular weight 6000), and 1.5 parts zinc stearate. The mixing process is the same as in Example 1, with the discharge temperature controlled at 120℃.

[0064] (2) Two-stage mixing:

[0065] Add 8.0 parts zinc diacrylate, 2.5 parts DCP, 0.2 parts CTP (anti-scorching agent), and 2.0 parts OBSH to a first-stage masterbatch. The mixing process is the same as in Example 1, and the discharge temperature is controlled at 88℃~90℃.

[0066] (3) Extrusion molding:

[0067] The temperature of the extruder in zones 1-2 is 95℃-100℃, the temperature of zones 3-4 is 130℃-135℃, the temperature of zone 5 is 155℃, and the die head temperature is set to 135℃.

[0068] (4) Foaming vulcanization:

[0069] The temperature zones of the sulfidation tunnel were set at 190℃, 215℃, and 220℃, with a dwell time of 240s to 300s. The dwell time was the same for each temperature zone. Finally, the material was naturally cooled to room temperature to obtain a microporous foamed sealing material.

[0070] Example 4:

[0071] This embodiment provides a method for preparing a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames. The component ratios and process steps are basically the same as in Embodiment 1, with the difference being:

[0072] In the first stage of intensive mixing, the mass fraction of zinc oxide was adjusted to 2.0 parts; in the second stage of mixing, the mass fraction of zinc diacrylate was adjusted to 4.0 parts. All other raw materials and process parameters remained the same as in Example 1.

[0073] Example 5:

[0074] This embodiment provides a method for preparing a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames. The component ratios and process steps are basically the same as in Embodiment 1, with the difference being:

[0075] In the first stage of intensive mixing, the mass fraction of zinc oxide was adjusted to 1.0 part; in the second stage of mixing, the mass fraction of zinc diacrylate was maintained at 5.0 parts. At this point, the mass ratio of zinc oxide to zinc diacrylate was 1:5. All other raw materials and process parameters remained the same as in Example 1.

[0076] Example 6:

[0077] This embodiment provides a method for preparing a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames. The component ratios and process steps are basically the same as in Embodiment 1, with the difference being:

[0078] During the extrusion molding stage, the die temperature was set to 140°C (i.e., 10°C lower than the temperature in zone 5). All other raw materials and process parameters remained the same as in Example 1.

[0079] Example 7:

[0080] This embodiment provides a method for preparing a lightweight, high-resilience microporous foamed sealing material for automotive door and window frames. The component ratios and process steps are basically the same as in Embodiment 1, with the difference being:

[0081] During the extrusion molding stage, the die temperature was set to 130°C (20°C lower than the temperature in zone 5). All other raw materials and process parameters remained the same as in Example 1.

[0082] Comparative Example 1:

[0083] Compared to Example 1, the difference is that zinc diacrylate (ZDA) is not added, and 5.0 parts of EPDM are added accordingly; otherwise, they are the same.

[0084] Comparative Example 2:

[0085] The difference from Example 1 is that polyethylene glycol (PEG) is not added; otherwise, they are the same.

[0086] Comparative Example 3:

[0087] The difference from Example 1 is that zinc stearate (ZnSt) is not added; otherwise, they are the same.

[0088] Comparative Example 4:

[0089] The difference from Example 1 is that the anti-scorching agent CTP is not added; otherwise, they are the same.

[0090] Comparative Example 5:

[0091] The difference from Example 1 is that the mass fraction of zinc oxide was adjusted to 3.0 parts (so that the mass ratio of ZnO:ZDA was 1:1.67), and all other parts were the same.

[0092] Comparative Example 6:

[0093] Compared with Example 1, the difference is that the die temperature in the extrusion molding stage is set to 160°C (i.e., the conventional heating extrusion strategy is implemented, and the die temperature is higher than that in the metering stage), while all other aspects are the same.

[0094] Test Example 1:

[0095] 1. Sample setup: The compound rubber obtained by two-stage mixing and left to stand at room temperature for 24 hours in each example and comparative example was taken as the test object. The sample amount was controlled at 25g±0.1g. Impurities that may exist on the surface were removed and the sample was ensured to be free of obvious pores.

[0096] 2. Test steps:

[0097] 2.1 The Mooney viscometer with alternating shear of a disc was used for testing. The instrument cavity was preheated and kept constant at 120°C.

[0098] 2.2 Place the prepared adhesive sample between the upper and lower cavities of the viscometer, close the cavity, and preheat at this temperature for 1 minute to ensure uniform temperature distribution inside the adhesive.

[0099] 2.3. Start the rotor and continuously record the Mooney viscosity change curve over time. Read the lowest Mooney viscosity value ML from the curve, and record the time t5 required for the viscosity to rise by 5 Mooney units from the lowest point, and the time t35 required for it to rise by 35 Mooney units. The results are shown in Table 1:

[0100] Table 1: Mooney scorch performance test data for each group of rubber compounds

[0101] Group Lowest Mooney viscosity ML(1+4)@120℃ Scorching time t5 (min) Scorching time t35 (min) Example 1 41.2 22.5 28.4 Example 2 40.5 23.8 29.6 Example 3 42.1 21.2 27.1 Example 4 41.8 22.1 27.9 Example 5 40.9 23.2 29.1 Example 6 41.5 22.4 28.2 Example 7 41.3 22.6 28.5 Comparative Example 1 48.5 14.2 19.5 Comparative Example 2 52.1 10.5 14.8 Comparative Example 3 50.3 12.8 17.6 Comparative Example 4 49.8 7.2 10.4 Comparative Example 5 47.6 13.5 18.2 Comparative Example 6 43.5 16.8 21.3

[0102] According to Table 1 and Figure 1The data shows that the scorch time (t5) of Examples 1-7 is within the range of 21.2 min to 23.8 min, exceeding that of all comparative examples. Among the comparative examples, Comparative Example 6, which performed best, had a t5 of only 16.8 min. This confirms the effectiveness of the synergistic intervention strategy of coordination modification and free radical capture in suppressing premature ion cluster formation, thus reserving sufficient thermal history margin for subsequent extrusion molding and uniform dispersion of the foaming agent. Examining the data fluctuations from a microscopic mechanism perspective, Comparative Example 4, after removing the anti-scorch agent CTP, experienced a sharp drop in t5 to 7.2 min. This confirms that in systems containing highly reactive metal salts such as zinc diacrylate (ZDA), if the primary free radicals generated by DCP decomposition are not effectively suppressed, they will rapidly induce early self-polymerization of ZDA and covalent cross-linking with the matrix. This early cross-linking behavior not only leads to a sharp increase in viscosity but also causes dead glue accumulation at the extruder die, severely disrupting the expansion space of the foaming gas. Meanwhile, Comparative Example 2, lacking the coordination protection of polyethylene glycol (PEG), showed a minimum Mooney viscosity of 52.1 and a significantly shortened scorch time. This phenomenon indicates that the ether oxygen atoms on the PEG molecular chain have a physical coordination shielding effect on zinc ions. Once this shield is missing, the polar monomer ZDA will generate microscopic local aggregation under the shear heat of a period of intense mixing, thereby increasing the internal frictional resistance of the melt and pushing up the macroscopic viscosity base. Comparing Example 1 and Comparative Example 6, it can be found that even with completely identical chemical compositions, Comparative Example 6, due to its failure to adopt the optimized process control flow of this solution, still exhibits significantly inferior scorch safety compared to the Example 1. This demonstrates that the present invention is not a simple additive composition, but rather achieves a deep coupling of low-viscosity rheological behavior and high scorch stability through precise control of the aggregation state of active ion clusters. This synergistic effect effectively solves the process problem of excessive sensitivity of highly active metal salt systems to thermal shear, ensuring the consistency of the physical properties of the compound under complex extrusion conditions.

[0103] Test Example 2:

[0104] 1. Sample setup: The finished microporous foamed sealing material products that had undergone the foaming and vulcanization stage and were naturally cooled to room temperature in each embodiment and comparative example were used as experimental subjects. The surface skin layer was avoided, and sections with intact internal pore structures were cut into regular fragments of about 2mm×2mm×2mm using a scalpel.

[0105] 2. Test steps:

[0106] 2.1 Accurately weigh approximately 0.5g of the sample and record it as the initial mass. Tightly wrap it in a 300-mesh stainless steel mesh of known mass to prevent leakage of fine carbon black particles that could interfere with the weighing.

[0107] 2.2 Place the wrapped sample in the extraction tube of a Soxhlet extractor and extract continuously for 48 hours under reflux with analytical grade toluene as solvent to fully dissolve uncrosslinked free rubber macromolecules, unreacted low molecular weight additives and paraffin oil.

[0108] 2.3. Take out the metal mesh containing the sample and place it in a vacuum drying oven. Bake it continuously at 60°C until the mass difference between two adjacent weighings is less than 0.002g to reach constant weight. Weigh the total mass after drying.

[0109] 2.4. After deducting the mass of the metal mesh and considering the mass fraction of insoluble inorganic fillers (such as carbon black, zinc oxide, etc.) in the formulation, the true percentage of gel content of the rubber matrix in the extraction residue was calculated. The results are shown in Table 2:

[0110] Table 2: Gel content test data of foamed sealing materials in each group

[0111] Group Initial sample mass (g) Residual mass after extraction (g) Gel content (%) Example 1 0.5012 0.4520 90.2 Example 2 0.4985 0.4421 88.7 Example 3 0.5036 0.4607 91.5 Example 4 0.5005 0.4494 89.8 Example 5 0.4978 0.4400 88.4 Example 6 0.5021 0.4544 90.5 Example 7 0.4993 0.4473 89.6 Comparative Example 1 0.5042 0.3448 68.4 Comparative Example 2 0.5011 0.3868 77.2 Comparative Example 3 0.4989 0.3816 76.5 Comparative Example 4 0.5025 0.3974 79.1 Comparative Example 5 0.5008 0.4071 81.3 Comparative Example 6 0.4996 0.4226 84.6

[0112] According to Table 2 and Figure 2The data shows that gel content directly characterizes the density and solvent resistance of the three-dimensional cross-linked network in the polymer system. Therefore, the example group exhibits a comprehensive advantage over all comparative examples in this indicator. Specifically, after soaking in boiling toluene for tens of hours, the gel content of the example samples generally remained stable in the high range of 88.4% to 91.5%. This strong network structure originates from the polyzinc diacrylate ion clusters formed by the in-situ polymerization of zinc diacrylate in the rubber matrix. These high-density physical cross-linking nodes are intertwined and fused with carbon-carbon covalent bonds induced by peroxides. In contrast, after completely stripping zinc diacrylate, the gel content of Comparative Example 1 plummeted to 68.4%. The sparse skeleton formed solely by peroxide cross-linking experienced a large number of chain segments slipping and untangling when faced with the strong penetration of high-temperature solvent molecules. Furthermore, the synergistic effect of each component in the formulation system significantly contributes to the final cross-linking. The influence of crosslinking was also significant. In Comparative Examples 2 and 3, which lacked polyethylene glycol and zinc stearate respectively, the gel content did not exceed 78%. At the same time, if polar monomers lack necessary interfacial compatibility and coordination shielding in a non-polar matrix, they are prone to local aggregation. This macroscopic dispersion heterogeneity directly led to a large loss of effective crosslinking nodes, and the imbalance of reaction kinetics further aggravated network defects. Specifically, Comparative Example 4 caused early scorching due to the lack of anti-scorching agent. Before extrusion, some dead gel was generated in the system. This dead gel was exposed to the unevenness and fragility of the internal network connection under strong solvent extraction, which reduced the gel content to 79.1%. In Comparative Example 5, which had an imbalanced zinc oxide ratio, the polymer chain segments were forcibly crosslinked before they had fully unfolded their conformation due to the excessively fast catalytic reaction, forming a gel content of only 81.3% containing a large number of free ends and voids. Even slight deviations in process parameters can be projected onto the final microscopic network phase. In Comparative Example 6, due to the failure to implement the inverted step temperature control strategy, the dynamic physical cross-linking of the extrudate, which was partially maintained by electrostatic attraction, failed to be rapidly cooled and locked when it was in a high-temperature state after leaving the die. This resulted in dissociation and recombination failure during the subsequent intense stretching of vulcanization expansion, leading to a lower extraction residual amount than in all examples.

[0113] Test Example 3:

[0114] 1. Sample Setup: A section approximately 50 mm in length was cut from the finished microporous foamed sealing material prepared in each embodiment and comparative example. A block sample weighing between 2 g and 3 g was cut using a sharp cutter. The skin layer on the sample surface was removed to eliminate the interference of the dense outer shell on the actual foaming rate, ensuring a smooth cut surface without any visible large pores or interconnected defects.

[0115] 2. Test steps:

[0116] 2.1 Environmental conditioning: The ambient temperature was controlled at around 23°C. An electronic analytical balance with an accuracy of 0.1 mg was used to accurately measure the mass of the sample in air and record it as m1.

[0117] 2.2 Medium preparation: Pour sufficient distilled water (density considered to be 1.00 g / cm³) into a glass container. 3 The sample is used as the impregnation medium. A metal sinker of known mass and volume is selected, and the sample is fixedly connected to the sinker with an extremely fine metal wire.

[0118] 2.3 Immersion Measurement: The sinker device carrying the sample is completely immersed in distilled water. After the balance reading stabilizes, the apparent mass in the suspended state is recorded. Note: The data read here has deducted the buoyancy effect generated by the sinker and metal wire in the liquid and is recorded as m2 (since the density of the foamed material is less than that of water, this value is negative, representing the net upward buoyancy).

[0119] 2.4 Calculation of Results: The sample volume V = m1 − m2 was calculated according to Archimedes' principle, and the apparent density ρ = m1 / V was then obtained. Five independent samples were tested in parallel for each formulation group, and the arithmetic mean was calculated. The results are shown in Table 3:

[0120] Table 3: Apparent density test data of microporous foamed sealing materials in each group

[0121] Group Mass of the sample in air (g) Apparent mass (g) of the sample in water <![CDATA[Calculate the apparent volume (cm 3） > <![CDATA[Apparent density (g / cm 3） > Example 1 2.1542 -2.3268 4.481 0.481 Example 2 2.0875 -2.4245 4.512 0.463 Example 3 2.3121 -2.2569 4.569 0.506 Example 4 2.1983 -2.3247 4.523 0.486 Example 5 2.2456 -2.4514 4.697 0.478 Example 6 2.1664 -2.2636 4.430 0.489 Example 7 2.1137 -2.3453 4.459 0.474 Comparative Example 1 2.5419 -1.0081 3.550 0.716 Comparative Example 2 2.4824 -1.3416 3.824 0.649 Comparative Example 3 2.6158 -1.2532 3.869 0.676 Comparative Example 4 2.5081 -1.3979 3.906 0.642 Comparative Example 5 2.4776 -1.1544 3.632 0.682 Comparative Example 6 2.3892 -1.4578 3.847 0.621

[0122] According to Table 3 and Figure 3 The data shows that the apparent density of the example group was stable between 0.463 and 0.506 g / cm³. 3 Significant weight reduction was achieved without increasing the amount of foaming agent. The core mechanism lies in the polar ion cluster network generated by the in-situ crosslinking of zinc diacrylate (ZDA) during the vulcanization stage, which endows the viscous rubber melt with extremely high interfacial tensile strength. During the high-temperature gas release stage, the bubble walls, supported by these dynamic physical nodes, can withstand significant bidirectional stretching without physical fracture. This strong and resilient elastic gas chamber structure effectively locks in the foaming gas, achieving full expansion of the macroscopic volume. In contrast, the weight reduction effects of the comparative examples were not ideal: in Comparative Example 1, the density rebounded to 0.716 g / cm³ after the absence of ZDA. 3 This confirms that a covalent framework alone is insufficient to bind high-pressure gas at high temperatures, leading to the escape of a large amount of gas. Furthermore, Comparative Example 3 lacked zinc stearate, resulting in an excessively high interfacial energy that raised the heterogeneous nucleation barrier, preventing the formation of dense honeycomb micropores. Comparative Example 6, lacking a stepped temperature control process, failed to establish initial strength through ion association during extrusion, leading to significant geometric shrinkage during subsequent vulcanization. In summary, this invention successfully resolves the contradiction between high-ratio foaming and pore wall stability through the precise coupling of covalent and physical dual-network construction with the extrusion process.

[0123] Test Example 4:

[0124] 1. Sample setup: Cylindrical samples with a height of about 10 mm and a diameter of about 29 mm were cut from the straight section of the finished microporous foamed sealing material product of each embodiment and comparative example after being naturally cooled to room temperature, or square samples with a length and width of about 25 mm were cut. Individuals with obvious visible depressions or pore defects on the end face were discarded.

[0125] 2. Test steps:

[0126] 2.1 Use a benchtop thickness gauge with an accuracy of 0.01 mm to measure the initial center height of the sample in a free state. Prepare two independent samples for each formulation group, one for room temperature and one for high temperature testing environments.

[0127] 2.2 Place the specimen in a constant compression device consisting of two parallel stainless steel plates. By placing a metal limiting block of a specific height between the steel plates, compress the specimen axially to 75% of its original height (i.e., generate 25% compressive strain), and tighten the bolts to lock the compression state.

[0128] 2.3 Place the two sets of compression devices loaded with the sample in a standard laboratory constant temperature environment of 23℃ and a forced convection hot air aging test chamber of 70℃ respectively, and let them stand for 22 hours.

[0129] 2.4 After the specified time has elapsed, remove the compression device from the high-temperature chamber and allow it to cool and stand at room temperature for 30 minutes. Then loosen all the fastening bolts of the device, remove the sample, and place it on a wooden flat pad at standard room temperature for 24 hours to recover freely.

[0130] 2.5. The final center height of the specimen was measured again using a benchtop thickness gauge. The compressive permanent deformation rate of the specimen was calculated based on the percentage of the difference between the initial and final height relative to the total initial compressive deformation. The results are shown in Table 4.

[0131] Table 4: Compression Permanent Deformation Test Data of Microporous Foamed Sealing Materials in Each Group

[0132] Group Compression set at room temperature (23℃) (%) High-temperature (70℃) compression set (%) Example 1 14.5 28.3 Example 2 13.8 26.9 Example 3 15.2 29.5 Example 4 14.1 27.8 Example 5 14.9 28.6 Example 6 14.6 28.9 Example 7 14.3 28.1 Comparative Example 1 26.8 58.4 Comparative Example 2 23.4 49.6 Comparative Example 3 24.1 51.2 Comparative Example 4 22.7 46.8 Comparative Example 5 25.5 53.7 Comparative Example 6 19.8 39.2

[0133] According to Table 4 and Figure 4The data shows that the compression set of the example groups was significantly lower than that of the corresponding comparative examples at both room temperature and 70°C, demonstrating excellent long-term deformation recovery capabilities. However, under the long-term closed operation of automotive door and window frames, the sealing material needs to withstand static compression for tens to hundreds of hours. Traditional purely chemically cross-linked foams are prone to irreversible slippage and breakage of molecular chains under the combined effects of long-term stress and thermo-oxidative stress, resulting in increased sealing gaps and problems such as wind noise and water leakage. In contrast, after complete stripping of zinc diacrylate, the high-temperature compression set of Comparative Example 1 at 70°C soared to 58.4%. The carbon-carbon covalent bonds, solely relying on peroxides, lack a stress dispersion mechanism under heat and pressure, and the macromolecular network skeleton under long-term deformation constraints undergoes permanent conformational changes and chain segment slippage. Examples 1 to 7 successfully constructed a covalent-physical dual-network structure by introducing an appropriate amount of ZDA, in which the zinc diacrylate ion clusters, as dynamic physical cross-linking nodes, exhibited mechanochemical properties of dissociation and recombination under stress. During long-term compression deformation, these high-density ionic bonds dissipate external deformation work through temporary bond breakage, thus protecting the main covalent network structure from macroscopic damage. After the external mechanical load is removed, due to the spatial topological memory effect of the covalent network, the broken polar ionic groups can approach each other again within the rubber matrix and recombine by electrostatic attraction, thereby providing additional rebound driving force and causing the sample thickness to rapidly approach the initial state. The uniformity of the microscopic distribution of the formulation system also directly reflects the lower limit of this elastic recovery. In Comparative Example 2 without polyethylene glycol and Comparative Example 3 without zinc stearate, the lack of spatial coordination shielding and interfacial tension regulation of polar metal ions led to local agglomeration and precipitation of ZDA in the nonpolar EPDM continuous phase. This microphase separation caused severe stress concentration under macroscopic load, and the weak points of the cell walls were prone to irreversible physical yielding and plastic folding after long-term compression, causing the room temperature deformation rate to climb to over 23%. Deviations in reaction kinetics also weaken the material's resilience. In Comparative Example 5, excessive zinc oxide disrupted the rate matching between vulcanization and foaming. The abnormally accelerated early curing forcibly fixed the polymer chain segments that were not yet fully stretched, leaving extremely high internal stress within the three-dimensional network. This internal stress accelerated the relaxation and aging of the polymer cross-linking network during subsequent continuous baking at 70°C. Even changes in the extrusion process can leave hidden dangers in the long-term mechanical properties of the product. Furthermore, in Comparative Example 6, due to the lack of instantaneous freezing and shaping intervention at the die head by inverted step temperature control, the polar network of the extrudate was not effectively locked in the initial stage of expansion after demolding. The residual thermal shrinkage effect, combined with the added mechanical compressive strain, further increased the final thickness loss ratio.

[0134] Test Example 5:

[0135] 1. Sample setup: Select the finished sealing materials of each embodiment and comparative example that have been foamed, vulcanized and completely cooled to room temperature. Cut along the longitudinal straight section of the material, use a slicer to remove the dense skin layer attached to the surface, retain the uniformly foamed core layer inside, and precisely grind its thickness to about 2.0 mm.

[0136] 2. Test steps:

[0137] 2.1 Using standard metal stamping dies, the above core layer slices are stamped into standard dumbbell-shaped specimens (for tensile performance testing) and right-angled or crescent-shaped specimens (for tear performance testing), and defective specimens with obvious notches on the cut edges or abnormal through holes inside are rejected.

[0138] 2.2. The thickness and width of the gauge length of the sample were measured at three different locations using a benchtop thickness gauge with an accuracy of 0.01 mm. The arithmetic mean of these measurements was taken as the reference data for calculating the cross-sectional area.

[0139] 2.3. The dumbbell-shaped specimen is symmetrically clamped in the upper and lower clamps of the electronic universal testing machine. The tensile separation speed of the clamp is set to 500 mm / min. The test is started and the maximum tensile force at the moment of specimen fracture and the elongation distance between the gauge lines are recorded in real time. The tensile strength and elongation at break are then calculated.

[0140] 2.4 Replace with a suitable tensile fixture and load a right-angled specimen. Maintain the same testing speed during the tear test, record the maximum load value during the tearing process, and divide it by the test thickness of the specimen to obtain the tear strength. For each test item, five independent specimens were tested in parallel for each group. After removing outlier values, the median value was recorded. The results are shown in Table 5:

[0141] Table 5: Test data of mechanical strength and tear resistance of microporous foamed sealing materials in each group

[0142] Group Tensile strength (MPa) Elongation at break (%) Tear strength (kN / m) Example 1 2.34 312.5 10.62 Example 2 2.15 294.8 9.87 Example 3 2.48 321.4 11.15 Example 4 2.27 308.2 10.43 Example 5 2.41 315.6 10.89 Example 6 2.31 305.1 10.51 Example 7 2.36 310.8 10.74 Comparative Example 1 1.18 175.4 4.53 Comparative Example 2 1.52 210.6 6.18 Comparative Example 3 1.45 204.3 5.86 Comparative Example 4 1.37 188.7 5.34 Comparative Example 5 1.64 225.2 6.82 Comparative Example 6 1.83 246.5 7.41

[0143] According to Table 5 and Figure 5The data shows that while reducing the apparent density of the material to achieve lightweighting, the example group still maintained excellent macroscopic mechanical properties. Its tensile strength was generally stable above 2.1 MPa, and its tear strength reached above 9.87 kN / m. However, after the zinc diacrylate was peeled off, the tensile strength and tear strength of Comparative Example 1 dropped sharply to 1.18 MPa and 4.53 kN / m, respectively. This is because the rigid network composed of carbon-carbon covalent bonds has a serious lack of energy dissipation path when dealing with macroscopic deformation. Once a small crack is generated at a single pore wall, it will quickly spread to the entire load-bearing section. The polyzinc diacrylate ion clusters formed after the introduction of zinc diacrylate can fundamentally change this destructive mechanical process. This is because these physical cross-linking points uniformly embedded in the rubber continuous phase have dynamic reversible characteristics. When the sample is subjected to external tensile or tearing stress, the polar ionic bonds will be preferentially broken in the form of sacrificial bonds, thereby inhibiting the breaking process of the backbone molecular chain by dissipating strain energy, thus giving the ultrathin foam pore wall extremely high toughness. Furthermore, the uniformity of the microstructure also interferes with whether the energy dissipation mechanism can completely cover the stressed area. Specifically, in Comparative Example 4, lacking the anti-scorching agent, and Comparative Example 2, lacking polyethylene glycol, both generated varying degrees of localized dead glue and large interconnected pores due to the loss of kinetic control in the early processing stage. These geometric abrupt changes at the micro level inevitably create stress concentration sources under external load conditions, leading to a sharp reduction in their elongation at break to about 200%. The imbalance of the surface tension gradient can also trigger a chain reaction. In Comparative Example 3, the uneven distribution of polar components in the matrix of the pore structure prevents the tensile tension from being uniformly transmitted between adjacent pore walls. Some pore walls bearing overload first undergo physical rupture, which then induces the overall tearing failure of the material. Even deviations in the extrusion temperature control process, such as the failure to perform reverse step cooling in Comparative Example 6, can lead to the pre-embedding of hidden microcracks inside the foamed preform due to the irregular release of stress within the polymer chain segments, ultimately resulting in a reduction in the load-bearing limit under extreme stress conditions.

[0144] Test Example 6:

[0145] 1. Sample setup: Extract the finished microporous foamed sealing materials from each example and comparative example that have been extruded, foamed and vulcanized and naturally cooled to room temperature (23°C). Place them on a flat test bench in a stress-free state for 24 hours to fully release the temporary mechanical stress that may have been introduced during the previous cutting process.

[0146] 2. Test steps:

[0147] 2.1. Cut a test strip of approximately 250 mm in length from each set of straight and undistorted finished sections. Using a dedicated white marker pen and a metal ruler, accurately mark two parallel reference lines 200 mm apart in the center area of ​​the sample surface.

[0148] 2.2 Prepare a high-temperature resistant, flat stainless steel tray with a polytetrafluoroethylene coating. Sprinkle a very thin layer of talcum powder evenly on the surface of the tray to minimize the frictional resistance between the sample and the bottom of the tray during the heat shrinkage process. Place the calibrated sample flat in the tray.

[0149] 2.3. Transfer the tray containing the sample into a preheated and stabilized forced convection hot air aging test chamber at 70°C and bake at a constant temperature for 24 hours.

[0150] 2.4 After the baking cycle, remove the tray and, together with the sample, allow it to cool statically in a standard laboratory environment at 23℃ for 2 hours. Then, use a vernier caliper with an accuracy of 0.02mm to remeasure the actual distance between the two baselines. Calculate the linear heat shrinkage rate of the sample based on the difference between the initial gauge length and the measured length. Three samples from each group were tested in parallel, and the average value was taken. The results are shown in Table 6:

[0151] Table 6: Test data on heat shrinkage rate of microporous foamed sealing materials in each group

[0152] Group Initial gauge length (mm) Length (mm) after baking at 70℃ Linear thermal shrinkage rate (%) Example 1 200.00 197.16 1.42 Example 2 200.00 197.44 1.28 Example 3 200.00 196.70 1.65 Example 4 200.00 197.32 1.34 Example 5 200.00 196.98 1.51 Example 6 200.00 197.06 1.47 Example 7 200.00 197.22 1.39 Comparative Example 1 200.00 188.32 5.84 Comparative Example 2 200.00 191.58 4.21 Comparative Example 3 200.00 190.66 4.67 Comparative Example 4 200.00 192.10 3.95 Comparative Example 5 200.00 190.36 4.82 Comparative Example 6 200.00 189.28 5.36

[0153] According to Table 6 and Figure 6Data shows that the linear heat shrinkage rates of Examples 1 to 7 remained between 1.2% and 1.7%, exhibiting good dimensional thermal stability. However, in polymer extrusion processes, the rubber melt undergoes shear deformation and molecular chain orientation as it passes through the die slit. Polymer chains oriented along the extrusion direction are prone to coiling and shrinking due to intensified thermal motion upon entering a high-temperature environment. Traditional foaming systems lack effective physical constraints between bubble expansion and chain segment relaxation, leading to easy shrinkage and deformation of the product in heated environments. Comparative Example 6 employed a conventional forward heating extrusion process without applying reverse step temperature control at the barrel end and die. The extrudate failed to rapidly establish a physical cross-linking network upon exiting the die, failing to effectively constrain the coiling of molecular chains. Residual extrusion shear stress was retained in the subsequent covalent vulcanization network and released under 70°C isothermal testing conditions, resulting in an irreversible heat shrinkage rate of 5.36%. Examples 1 to 7 employ a stepped temperature control strategy at the extrusion end to reduce the demolding temperature, promoting physical association of zinc diacrylate (ZDA) ion clusters during demolding. This fixes the spatial structure of the oriented chain segments and effectively counteracts thermal shrinkage stress. Furthermore, changes in formulation components significantly affect the thermal stability of the material. Comparative Example 1, without the addition of ZDA, relies solely on peroxides to form a covalent cross-linked network. At 70°C, its chain segment slip activity is high, and due to the lack of physical cross-linking nodes, the material undergoes irreversible deformation, with a linear shrinkage rate approaching 6%. The dispersion state of polar additives also affects the uniformity of internal stress release. Comparative Example 2, without the addition of polyethylene glycol, weakens the physical coordination effect on zinc ions, leading to localized agglomeration of ZDA and an uneven distribution of the physical cross-linked network within the matrix. This discontinuous structure cannot provide uniform deformation constraint; weak areas with stress concentration are prone to deformation during heating, resulting in increased overall shrinkage of the sample. The data above show that the synergistic effect of the formulation components of this invention, combined with the inverted step temperature control process, can effectively resist thermal stress relaxation and improve the dimensional stability of foamed sealing products.

[0154] Test Example 7:

[0155] 1. Sample setup: The finished sealing materials of each embodiment and comparative example, which have been extruded, foamed and vulcanized and left at room temperature for more than 24 hours, were selected as experimental subjects. A special double-sided cutter was used to longitudinally cut them, completely removing the dense skin layer on the surface of the sample to expose the internal microporous foam core layer. The samples were then precisely cut into block samples with a length of about 50 mm, a width of about 20 mm, uniform thickness and no macroscopic tear defects.

[0156] 2. Test steps:

[0157] 2.1 Place all pretreated samples in a standard environmental chamber with a temperature controlled at 23℃ and a relative humidity set at 50% for 24 hours to condition them and eliminate residual moisture and processing stress inside the material.

[0158] 2.2 After the conditioning is completed, use an analytical balance with an accuracy of 0.1 mg to weigh the initial mass of each sample and mark them one by one on the data recording table.

[0159] 2.3 Prepare a constant temperature water bath with sufficient volume and fill it with degassed distilled water, maintaining the water temperature at 23℃. Completely immerse the sample below the water surface. Due to the high buoyancy of the foaming material, use a stainless steel mesh of known weight that does not absorb water to press the sample down to about 50mm below the water surface, ensuring that all exposed surfaces of the sample are in full contact with the water.

[0160] 2.4 After the sample has been soaked in distilled water for 24 hours, remove it and gently blot the free water droplets on the surface of the sample with slightly damp lint-free filter paper or medical absorbent cotton. This wiping process must be completed within 1 minute after removal to prevent the water adsorbed in the internal pores from seeping out in reverse.

[0161] 2.5 Immediately after wiping, transfer the sample to an analytical balance and weigh its wet mass after immersion. Calculate the percentage of water absorption by mass based on the ratio of the mass difference before and after immersion to the initial mass. Five samples were tested in parallel for each test group, and the arithmetic mean of the results was taken. The results are shown in Table 7:

[0162] Table 7: Static water absorption rate test data of microporous foamed sealing materials in each group

[0163] Group Initial mass (g) before testing Wet weight after soaking (g) Static water absorption rate (%) Example 1 1.8421 1.8653 1.26 Example 2 1.7954 1.8239 1.59 Example 3 1.9102 1.9315 1.11 Example 4 1.8536 1.8801 1.43 Example 5 1.8845 1.9082 1.26 Example 6 1.8219 1.8465 1.35 Example 7 1.8608 1.8844 1.27 Comparative Example 1 2.1456 2.5081 16.89 Comparative Example 2 1.9842 2.1707 9.40 Comparative Example 3 2.0518 2.2736 10.81 Comparative Example 4 1.9564 2.1152 8.12 Comparative Example 5 2.0135 2.2573 12.11 Comparative Example 6 1.9127 2.2158 15.85

[0164] According to Table 7 and Figure 7Data shows that the static water absorption rates of Examples 1 to 7 remained between 1.1% and 1.6%, indicating that a structurally complete independent closed-cell phase was formed inside the material. In practical applications of automotive door and window sealing systems, high water absorption rates not only lead to the risk of leakage in the cabin during the rainy season, but also cause physical tearing and damage to the rubber matrix due to the expansion of water freezing in the pores during winter. Furthermore, the structure of the cross-linked network directly determines the closed-cell rate of the bubbles. The examples improved the tensile toughness of the viscous melt by generating zinc diacrylate ion clusters in situ within the rubber matrix. This physical ion network effectively supports the expansion of bubbles, stably sealing the foaming gas within independent micropores and cutting off the channels for external water penetration. Conversely, Comparative Example 1, without the addition of zinc diacrylate, lacked sufficient melt tensile strength due to the covalent cross-linked network constructed solely from peroxides during the high-temperature foaming stage. When the foaming agent rapidly decomposed, the pore walls could not withstand the gas expansion pressure and ruptured over a large area. The ruptured pores interconnected to form a capillary network, making it easy for water to penetrate, resulting in a water absorption rate as high as 16.89%. Meanwhile, the dispersion state of micro-components and the degree of matching with reaction kinetics also affect the integrity of the bubbles. Comparative Example 3, without the addition of zinc stearate, lacked control over the interfacial tension of the polar system, resulting in a high nucleation free energy. Some nucleated bubbles merged during expansion, forming thin-walled and large-volume pores. These weak pore walls were prone to rupture due to stress concentration during the cooling and shrinkage phase, causing the water absorption rate to rise to 10.81%. In Comparative Example 5, the excessive zinc oxide led to premature vulcanization, and the cross-linked network was already formed before the foaming gas was fully released. After demolding, the residual high-pressure gas inside broke through the not-yet-completely-cooled rubber matrix, producing microscopic tear textures and increasing the risk of moisture intrusion. Furthermore, extrusion process parameters play a crucial role in constraining the stability of the pore wall structure. Comparative Example 6 did not employ a stepped temperature control strategy, and the extrudate failed to rapidly establish a physical association network at the high temperature of demolding. During the cooling process, the high-temperature melt inside undergoes uneven volume shrinkage. Due to the lack of surface strength support, adjacent cell walls are squeezed and ruptured under shrinkage stress, resulting in a macroscopic water absorption rate of 15.85%. Therefore, the test data shows that by constructing a covalent and physical dual cross-linked network and combining it with an inverted step temperature control process, cell rupture and connectivity defects during the foaming process can be effectively suppressed, thereby improving the closed-cell rate and waterproof performance of the sealing material.

[0165] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A lightweight, high-resilience microporous foam sealing material for automotive door and window frames, characterized in that, Includes the following weight groups: EPDM rubber: 100 parts; Carbon black: 40.0–60.0 parts; Paraffin oil: 40.0–70.0 parts; Zinc oxide: 1.0–2.0 parts; Stearic acid: 1.0 part; Polyethylene glycol: 0.5–2.0 parts; Zinc stearate: 1.5–3.0 parts; Zinc diacrylate: 3.0–8.0 parts; Dicoumir peroxide: 1.5–2.5 parts; CTP (Cytochlor) anti-scorching agent: 0.2–0.5 parts; 4,4'-Oxobisbenzenesulfonylhydrazine: 2.0–4.0 parts.

2. The foamed sealing material according to claim 1, characterized in that, The ethylene propylene diene monomer (EPDM) rubber contains 55wt% to 70wt% ethylene repeating units, 4wt% to 9wt% diene monomer (ENB) repeating units, and Mooney viscosity ML(1+4)@125℃ is 60 to 80; the polyethylene glycol has a weight-average molecular weight of 4000 to 6000 and a hydroxyl value of 18mgKOH / g to 28mgKOH / g.

3. The foamed sealing material according to claim 1, characterized in that, The zinc diacrylate is a white powder with a median diameter (D50) of 5 μm to 15 μm and a purity of ≥98%; the scorching inhibitor CTP is N-cyclohexylthiophthalimide.

4. The foamed sealing material according to claim 1, characterized in that, The decomposition temperature of the 4,4'-oxobisbenzenesulfonyl hydrazine is 155℃~165℃, the gas emission rate is 120ml / g~130ml / g, and the average particle size is 5μm~10μm.

5. The foamed sealing material according to claim 1, characterized in that, The apparent density of the material is 0.463 g / cm³. 3 ~0.506g / cm 3 The percentage of the actual gel content of the rubber matrix in the extracted residue was 88.4% to 91.5%.

6. A preparation method for preparing the lightweight, high-resilience microporous foamed sealing material for automotive door and window frames as described in claim 1, characterized in that, Includes the following steps: S1, First stage of internal mixing: EPDM rubber, carbon black, paraffin oil, zinc oxide, stearic acid, polyethylene glycol and zinc stearate are put into an internal mixer and mixed. After the rubber is discharged, it is naturally cooled to obtain the first stage of masterbatch. S2, Two-stage mixing: The first stage of masterbatch obtained in step S1 is put into a two-roll mill, and zinc diacrylate, dicoumir peroxide, anti-scorching agent CTP and 4,4'-oxobisbenzenesulfonyl hydrazine are added in sequence for mixing. The mixed rubber is then discharged to obtain the finished product. S3. Extrusion molding: The compound rubber product obtained in step S2 is fed into a single screw extruder for extrusion. Step temperature control is performed, and the die temperature is set to be 10℃~20℃ lower than the metering section temperature of the extruder to obtain the extruded preform. S4. Foaming and vulcanization: The extruded preform obtained in step S3 is fed into a normal pressure hot air vulcanization tunnel for foaming and vulcanization. Finally, after cooling to room temperature, the foamed sealing material is obtained.

7. The preparation method according to claim 6, characterized in that, In step S1, the initial speed of the internal mixer is set to 40 rpm to 45 rpm and the initial temperature is 50°C. When the material is heated to 110°C to 120°C under shear heat, it is kept mixed for 2 min to 3 min, and then the glue is discharged and the material is controlled to cool down naturally to 30°C to 40°C.

8. The preparation method according to claim 6, characterized in that, In step S2, the roller temperature of the open mill is controlled at 45℃~55℃; after the material is added, the material is first fed and packaged, and then cut by the left and right cutters 3 to 5 times each, and the discharge temperature is controlled at 80℃~90℃.

9. The preparation method according to claim 6, characterized in that, In step S3, the length-to-diameter ratio of the single screw extruder is 16; the temperature of the extruder is set to 85℃~100℃ for zones 1 and 2, 120℃~135℃ for zones 3 and 4, 145℃~155℃ for zone 5 (metering section), and 130℃~140℃ for the die.

10. The preparation method according to claim 6, characterized in that, In step S4, the atmospheric pressure hot air vulcanization tunnel is a three-section temperature zone, with each section temperature zone set to 180℃~190℃, 200℃~215℃, and 210℃~220℃ respectively; the total residence time of the material in the tunnel is 240s~390s, and the residence time in each temperature zone is the same.

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