Gradient vulcanization preparation method of rubber sealing strip for automobile

Abstract

The invention discloses a gradient vulcanization preparation method of a rubber sealing strip for an automobile, and relates to the technical field of automobile part manufacturing. The multi-layer structure blank comprises a functional outer layer, a first composite layer of a high-melting-point phase change material and an electrogenerated shape memory polymer, a second composite layer of a low-melting-point phase change material and a thermogenerated shape memory polymer, a core layer containing an induction medium and a functional inner layer. Through step-by-step control of core layer pilot vulcanization and outer layer synergistic vulcanization and in combination with directional infrared energy supplementation, the contradiction between insufficient corner vulcanization and overheating degradation of the core layer is solved, and the overall vulcanization uniformity of the product is ensured. By means of the synergistic effect of the shape memory polymer and the phase change material, gradient pulse cooling and post-treatment shaping are matched, vulcanization internal stress is effectively released, the product straightness and size stability are remarkably improved, and the deformation risk is reduced.

Description

Technical Field

[0001] This invention relates to the field of automotive parts manufacturing technology, and in particular to a gradient vulcanization preparation method for automotive rubber sealing strips. Background Technology

[0002] As a critical sealing component, automotive rubber sealing strips directly impact the user experience and safety of vehicles due to their sealing performance, durability, and dimensional accuracy. Existing rubber sealing strip vulcanization processes often employ either simultaneous overall vulcanization or an outside-to-inside heat conduction vulcanization mode. However, due to limitations in heat transfer characteristics, achieving precise temperature matching between the core and outer layers is difficult.

[0003] In traditional processes, special areas such as edges and corners suffer from low hot air energy absorption efficiency due to their geometric structure, making them prone to incomplete vulcanization. Meanwhile, the core layer may experience overheating and degradation due to heat accumulation, resulting in cross-linking network defects. Furthermore, large temperature fluctuations during vulcanization can easily lead to stress concentration in the product, causing subsequent deformation and straightness deviations. In addition, existing processes lack real-time monitoring and adaptive adjustment of material distribution uniformity, resulting in poor product performance consistency and low energy utilization efficiency, making it difficult to meet the high-precision, high-performance production requirements of automotive parts. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a gradient vulcanization method for preparing automotive rubber sealing strips. The technical solution is as follows: A gradient vulcanization preparation method for automotive rubber sealing strips includes the following steps: Step 1: A multi-layer preform is formed by co-extrusion using a variable cross-section composite extruder. The multi-layer preform includes a functional outer layer, a first composite layer of high-melting-point phase change material and electro-induced shape memory polymer, a second composite layer of low-melting-point phase change material and thermo-induced shape memory polymer, a core layer containing a sensing medium, and a functional inner layer. Step 2: The multi-layered preform is pretreated by ultrasound and then shaped by cooling in a 5℃-15℃ bath. Step 3: A segmented medium-frequency induction and ultrasonic composite device is used. Through the synergistic effect of medium-frequency induction and ultrasound, the core layer containing the induction medium is heated to 180℃-205℃ and pilot vulcanization is completed, while the temperature of other layers is maintained at 110℃-130℃. Step 4: Under the action of front hot air at 200℃-220℃ and rear hot air at 180-190℃, combined with directional infrared energy supplementation, the temperature is controlled by the electro-induced shape memory polymer composite layer, so that the functional outer layer can be fully vulcanized. Step 5: The sealing strip passes through a cooling tunnel and is sequentially cooled by a first-gradient temperature ethylene glycol solution, a second-gradient temperature deionized water solution, and a third-gradient temperature air solution. This is combined with pulse mode spraying and stopping spraying to achieve gradual cooling of the sealing strip. Step 6: Keep the sealing strip in a constant temperature shaping chamber at 170℃-180℃ for 3-5 minutes, and then cool it to room temperature at the set cooling rate to fix the shape memory polymer into its final shape.

[0005] Optionally, the core layer containing the sensing medium in step 1 is EPDM rubber mixed with 5wt%-8wt% nano-soft magnetic ferrite particles and 0.3wt%-0.5wt% vulcanization accelerator TMTD, the functional outer layer is a blended layer of EPDM and PER lubricant, and the functional inner layer is a composite layer of EPDM and nanofibers. The phase transition temperature of high-melting-point phase change materials is 190-210℃, and the phase transition temperature of low-melting-point phase change materials is 150-160℃; electro-induced shape memory polymers contain 2.8wt%-3.1wt% conductive carbon black, and the glass transition temperature of thermo-induced shape memory polymers is 160℃-170℃.

[0006] Optionally, in step 2, the extruded multilayer structure preform is first subjected to a 20kHz-40kHz ultrasonic pretreatment device with an ultrasonic power of 500W-800W to disperse the agglomerated magnetic media particles through cavitation effect for 3-5 seconds; then it is placed in a 5℃-15℃ ethylene glycol aqueous solution cooling bath for shaping, with the cooling time controlled at 10-15 seconds.

[0007] Optionally, in step 2, the preform after ultrasonic pretreatment is monitored by both a mechanical energy dielectric constant scanner and a near-infrared spectrometer. If the dielectric constant fluctuation monitored by the dielectric constant scanner is less than or equal to the set fluctuation threshold, it is considered qualified. The near-infrared spectrometer judges the dispersion uniformity of the shape memory polymer and phase change material by the intensity of characteristic peaks. If the dispersion uniformity is greater than or equal to the uniformity threshold, it is considered qualified. After both the dielectric constant fluctuation and dispersion uniformity are qualified, the process proceeds to step 3.

[0008] Optionally, in step 3, the first segment of the segmented intermediate frequency induction ultrasonic composite device uses 10kHz-50kHz intermediate frequency induction combined with 20kHz ultrasound, and the second segment uses 50kHz-200kHz intermediate frequency induction combined with 30kHz ultrasound, with an ultrasonic power of 500W-1000W.

[0009] Optionally, in step 3, the first core layer of the intermediate frequency induction ultrasonic composite device is heated to 180℃-200℃, and the ultrasonic vibration accelerates the movement of molecular chains, thereby improving the uniformity of the crosslinking reaction; the second composite layer absorbs heat, and the outer layer temperature is maintained at 110℃-130℃, so that the shape memory polymer retains its initial shape. The second core layer is kept at 190℃-205℃, and the ultrasonic power is increased to 1000W to eliminate cross-linking network defects.

[0010] Optionally, completing the full vulcanization in step 4 includes the following steps: Step 41: The sealing strip enters the zoned temperature-controlled hot air vulcanizing box. The front hot air temperature is 200℃-220℃. At the same time, the directional infrared energy replenishment device is turned on. Based on the monitoring data of the near-infrared spectroscopy monitor in Step 2, infrared energy with an energy density of 100W / cm²-150W / cm² is output to the corners. Step 42: The high-melting-point phase change material and the first composite layer of the electro-induced shape memory polymer undergo a phase change, absorbing heat to stabilize the surface temperature at 190℃-210℃. The electro-induced shape memory polymer maintains the vulcanization required shape under the action of temperature, avoiding deformation. Step 43: The sealing strip enters the rear hot air zone, and the hot air temperature is adjusted to 180℃-190℃. The temperature is maintained for 5-8 seconds. The first composite layer and the second composite layer release the latent heat of phase change simultaneously, which continuously provides stable heat for the cross-linking reaction of the functional outer layer, ensuring that the cross-linking degree of the functional outer layer reaches more than 85%.

[0011] Optionally, the formula for calculating the directional energy replenishment density in step 41 is: ; in It is the energy density of directional energy replenishment. The target vulcanization energy density is determined by the energy per unit area required for the functional outer layer to achieve 85% crosslinking. It is the effective energy density of hot air. It is the edge and corner geometric correction factor. It is the material distribution uniformity coefficient. It's the safety factor.

[0012] Optionally, in step 5, the cooling tunnel is divided into three sections, using 10°C ethylene glycol solution, 25°C deionized water, and 40°C air as cooling media respectively, to form a temperature gradient. The spray system adopts a pulse mode of 15 seconds of spraying and 10 seconds of stopping, with a spray pressure of 0.3MPa-0.5MPa; A temperature sensor is installed at the cooling end. When the temperature of the sealing strip drops to 80℃, a weak electric field of 10kV / m-20kV / m is turned on to trigger the shape recovery of the electro-induced shape memory polymer.

[0013] Optionally, the final product has a tensile strength greater than or equal to 15 MPa, an elongation at break greater than or equal to 400%, a sealing pressure deviation less than or equal to ±0.02 MPa, and a straightness error less than or equal to 0.1 mm / m.

[0014] In summary, the present invention has at least one of the following beneficial technical effects: This invention provides a gradient vulcanization preparation method for automotive rubber sealing strips. By controlling the stepwise vulcanization of the core layer and the synergistic vulcanization of the outer layer, combined with directional infrared energy supplementation, the contradiction between insufficient vulcanization at the edges and corners and overheating degradation of the core layer is resolved, ensuring the overall vulcanization uniformity of the product.

[0015] By leveraging the synergistic effect of shape memory polymers and phase change materials, combined with gradient pulse cooling and post-treatment shaping, vulcanization internal stress is effectively released, significantly improving product straightness and dimensional stability, and reducing the risk of deformation.

[0016] Integrating ultrasonic pretreatment, dual monitoring, and adaptive energy calculation improves material dispersion uniformity and process controllability, enabling the product to achieve high standards in mechanical properties such as tensile strength and elongation at break, as well as sealing pressure stability.

[0017] The combination of multi-field coupling and smart materials optimizes the energy transfer path and reduces ineffective energy consumption. At the same time, the closed-loop control system improves production consistency and reduces the defect rate, demonstrating good industrial application value. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of the gradient vulcanization preparation method for automotive rubber sealing strips of the present invention; Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings.

[0020] This invention discloses a gradient vulcanization preparation method for automotive rubber sealing strips.

[0021] Reference Figure 1 Example 1, a gradient vulcanization preparation method for automotive rubber sealing strips, includes the following steps: Step 1: A multi-layer preform is formed by co-extrusion using a variable cross-section composite extruder. The multi-layer preform includes a functional outer layer, a first composite layer of high-melting-point phase change material and electro-induced shape memory polymer, a second composite layer of low-melting-point phase change material and thermo-induced shape memory polymer, a core layer containing a sensing medium, and a functional inner layer. Step 2: The multi-layered preform is pretreated by ultrasound and then shaped by cooling in a 5℃-15℃ bath. Step 3: A segmented medium-frequency induction and ultrasonic composite device is used. Through the synergistic effect of medium-frequency induction and ultrasound, the core layer containing the induction medium is heated to 180℃-205℃ and pilot vulcanization is completed, while the temperature of other layers is maintained at 110℃-130℃. Step 4: Under the action of front hot air at 200℃-220℃ and rear hot air at 180-190℃, combined with directional infrared energy supplementation, the temperature is controlled by the electro-induced shape memory polymer composite layer, so that the functional outer layer can be fully vulcanized. Step 5: The sealing strip passes through a cooling tunnel and is sequentially cooled by a first-gradient temperature ethylene glycol solution, a second-gradient temperature deionized water solution, and a third-gradient temperature air solution. This is combined with pulse mode spraying and stopping spraying to achieve gradual cooling of the sealing strip. Step 6: Keep the sealing strip in a constant temperature shaping chamber at 170℃-180℃ for 3-5 minutes, and then cool it to room temperature at the set cooling rate to fix the shape memory polymer into its final shape.

[0022] By adopting the above technical solution, a multi-layered structure enables zoned regulation, and a functionally defined layered design forms the basis for vulcanization regulation. The core layer containing the sensing medium provides a carrier for internal energy excitation; the first and second composite layers utilize the heat storage and release characteristics of phase change materials to achieve temperature buffering; the electro- and thermo-induced shape memory polymers undertake the functions of shape maintenance and correction; and the functional outer and inner layers ensure the final performance. All layers work together to create structural conditions for gradient vulcanization.

[0023] Multi-field synergy enables directional energy transfer, breaking the limitations of traditional single-heat conduction in vulcanization. Mid-frequency induction energy is precisely applied to the induction medium of the core layer, causing it to heat up preferentially to complete pilot vulcanization. Ultrasonic vibration assists in optimizing molecular chain motion and improving the uniformity of cross-linking in the core layer. Subsequently, hot air provides the basic energy for vulcanization in the outer layer, and directional infrared radiation provides energy supplementation to the corner areas, forming a core excitation, outer layer energy supplementation, and energy distribution mode, solving the problem of energy supply and demand imbalance in different regions.

[0024] Smart materials dynamically regulate the vulcanization process, balancing temperature stability and morphological integrity. Low-melting-point phase change materials absorb excess heat during the core layer vulcanization stage, preventing premature vulcanization of the outer layer; high-melting-point phase change materials stabilize the surface temperature during the external vulcanization stage, preventing local overheating or temperature fluctuations; shape memory polymers maintain a preset shape throughout the vulcanization process, and shape recovery is triggered by a weak electric field during the cooling stage, correcting dimensional deviations and achieving precise dual control of temperature and morphology.

[0025] The gradient process optimizes the vulcanization and shaping effects, reducing internal stress and performance defects. Gradient cooling achieves a smooth transition of the sealing strip from a high-temperature vulcanized state to a room-temperature state by gradually decreasing the temperature of the cooling medium. Combined with a pulse spray mode, it further alleviates the internal stress caused by the temperature gradient. Post-treatment shaping uses precise temperature control and heat preservation and cooling to fix the shape memory polymer in its final shape, ensuring the straightness and dimensional accuracy of the product, ultimately achieving a synergistic improvement in mechanical properties, sealing performance, and dimensional stability.

[0026] Example 2: The core layer containing the sensing medium in step 1 is EPDM rubber mixed with 5wt%-8wt% nano-soft magnetic ferrite particles and 0.3wt%-0.5wt% vulcanization accelerator TMTD. The functional outer layer is a blended layer of EPDM and PER lubricant, and the functional inner layer is a composite layer of EPDM and nanofiber. The phase transition temperature of high-melting-point phase change materials is 190-210℃, and the phase transition temperature of low-melting-point phase change materials is 150-160℃; electro-induced shape memory polymers contain 2.8wt%-3.1wt% conductive carbon black, and the glass transition temperature of thermo-induced shape memory polymers is 160℃-170℃.

[0027] By adopting the above technical solution, the core layer material components are adapted to internally activated vulcanization. EPDM rubber, as the substrate, provides basic elasticity and weather resistance. The nano-soft magnetic ferrite particles possess excellent electromagnetic induction response capabilities, efficiently absorbing mid-frequency induced energy and converting it into heat energy, enabling the core layer to rapidly heat up and achieve pilot vulcanization. The vulcanization accelerator TMTD can accelerate the cross-linking reaction of the core layer rubber molecular chains, shorten the vulcanization time, and improve the cross-linking density and structural stability of the core layer.

[0028] The functional layer materials are specifically optimized for performance. The outer functional layer uses a blend of EPDM and PER lubricant. The PER lubricant reduces the surface friction coefficient and improves the installation compatibility and wear resistance of the sealing strip. The inner functional layer uses a composite of EPDM and nanofibers. The nanofibers enhance the structural strength and tear resistance of the inner layer. Both materials ensure the product's service performance from the perspectives of surface use and internal support.

[0029] The phase change material temperature parameters match the requirements of the vulcanization stage. The phase change temperature of the low-melting-point phase change material matches the temperature range during the pilot vulcanization of the core layer, which can efficiently absorb the excess heat transferred by the core layer and stabilize the outer layer temperature within the pre-vulcanization range, thus preventing premature cross-linking of the outer layer. The phase change temperature of the high-melting-point phase change material is consistent with the target temperature for full vulcanization of the outer layer. It can absorb excess heat during the hot air and infrared energy replenishment stages, maintain a constant surface temperature, and ensure that the cross-linking reaction of the outer layer proceeds uniformly.

[0030] Shape memory polymers are adapted to shape control based on their composition and properties. Electroactive shape memory polymers are given electric field responsiveness by the added conductive carbon black, which, combined with the temperature and weak electric field triggering during the vulcanization and cooling stages, enables shape maintenance and precise correction. The glass transition temperature of thermoactive shape memory polymers is matched with the key temperature nodes of the vulcanization process. During the initial vulcanization of the core layer, the initial shape is maintained to avoid structural distortion. The final shape is then fixed by temperature control to ensure the dimensional accuracy of the product.

[0031] The content range of each material component has been precisely calibrated. The addition of nano-soft magnetic ferrite particles, vulcanization accelerators, conductive carbon black, etc., ensures that their core functions are fully utilized without affecting the performance of the substrate itself. The characteristic parameters of phase change materials and shape memory polymers are precisely matched with process temperature and electric field conditions to form a closed-loop adaptation of material characteristics, process parameters, and product performance, ultimately achieving synergistic optimization of gradient vulcanization effect and overall product performance.

[0032] In Example 3, in step 2, the extruded multilayer structure preform is first subjected to an ultrasonic pretreatment device with a power of 500W-800W at a frequency of 20kHz-40kHz. The agglomerated magnetic media particles are dispersed by the cavitation effect, and the treatment time is 3-5s. Then, it is placed in a 5℃-15℃ ethylene glycol aqueous solution cooling bath for shaping, and the cooling time is controlled at 10-15s.

[0033] In Example 4, in step 2, the preform after ultrasonic pretreatment is monitored by both a mechanical energy dielectric constant scanner and a near-infrared spectrometer. The dielectric constant fluctuation monitored by the dielectric constant scanner is less than or equal to the set fluctuation threshold and is considered qualified. The near-infrared spectrometer judges the dispersion uniformity of the shape memory polymer and phase change material by the intensity of characteristic peaks. The dispersion uniformity is greater than or equal to the uniformity threshold and is considered qualified. After both the dielectric constant fluctuation and dispersion uniformity are qualified, the process proceeds to step 3.

[0034] By employing the above technical solution, material dispersion is optimized and the multilayer structure is fixed. The combination of an ultrasonic frequency of 20kHz-40kHz and a power of 500W-800W generates periodic pressure fluctuations within the rubber preform, forming numerous microbubbles. The cavitation effect when these bubbles burst effectively breaks up agglomerates of nano-soft magnetic ferrite particles, ensuring uniform distribution of the sensing medium within the core layer. This is a prerequisite for uniform transfer of subsequent mid-frequency induction energy and consistent heating of the core layer. A processing time of 3-5 seconds ensures effective dispersion while preventing excessive ultrasonic energy input that could lead to rubber molecular chain breakage. Subsequent cooling with a 5℃-15℃ ethylene glycol aqueous solution utilizes its low freezing point and excellent thermal conductivity to rapidly remove heat from the preform, quickly solidifying the extruded high-temperature rubber. This fixes the interlayer interfaces and dimensional morphology of the multilayer structure, preventing structural distortion due to its own weight or external forces during transport. A cooling time of 10-15 seconds balances cooling efficiency and energy consumption, ensuring the preform hardness meets the requirements for subsequent processing.

[0035] A quality threshold is established through dual-parameter monitoring to eliminate preforms with abnormal material distribution, thus avoiding subsequent vulcanization defects. A dielectric constant scanner indirectly reflects the uniformity of the distribution of nano-soft magnetic ferrite particles by detecting fluctuations in the dielectric properties of the core layer. Uneven distribution of the sensing medium can lead to localized temperature deviations during subsequent mid-frequency induction heating, causing inconsistent vulcanization. Therefore, setting a fluctuation threshold can screen out preforms with acceptable medium dispersion. A near-infrared spectroscopy analyzer quantifies the dispersion state of shape memory polymers and phase change materials in the composite layer by identifying the characteristic peak intensities. Aggregation or segregation of these functional materials weakens their temperature regulation and morphology maintenance functions; setting a uniformity threshold ensures the stability of the composite layer performance. Preforms that pass both monitoring tests proceed to subsequent processes, reducing product performance fluctuations caused by material inhomogeneity from the source and improving overall production consistency and yield.

[0036] Example 5: In step 3, the first segment of the segmented intermediate frequency induction ultrasonic composite device uses 10kHz-50kHz intermediate frequency induction and 20kHz ultrasound in synergy, and the second segment uses 50kHz-200kHz intermediate frequency induction and 30kHz ultrasound in synergy, with an ultrasonic power of 500W-1000W.

[0037] In Example 6, the first core layer of the intermediate frequency induction ultrasonic composite device in step 3 is heated to 180℃-200℃. The ultrasonic vibration accelerates the movement of molecular chains, thereby improving the uniformity of the crosslinking reaction. The second composite layer absorbs heat, and the outer layer temperature is maintained at 110℃-130℃, so that the shape memory polymer retains its initial shape. The second core layer is kept at 190℃-205℃, and the ultrasonic power is increased to 1000W to eliminate cross-linking network defects.

[0038] By employing the above technical solution, precise targeted energy transfer and synergistic enhancement are achieved through a segmented combination of frequency and power. The first segment uses a 10kHz-50kHz mid-frequency induction, where the electromagnetic energy has a deep skin effect, penetrating to the core layer containing the induction medium and efficiently exciting the nano-soft magnetic ferrite particles to generate heat. This is combined with 20kHz ultrasound, whose vibration frequency matches the motion characteristics of the rubber molecular chains, helping to disperse localized energy accumulation. The second segment uses a higher mid-frequency induction of 50kHz-200kHz, with stronger energy focusing, further improving the temperature stability of the core layer. The 30kHz ultrasound frequency is higher, with more concentrated vibration energy, enhancing the mobility of the molecular chains. The 500W-1000W ultrasonic power range ensures both the promotion of the cross-linking reaction and avoids excessive power leading to rubber degradation. This two-stage parameter combination forms a deep heating-precise heat preservation energy supply mode, adapting to the different stages of core layer pilot vulcanization requirements.

[0039] By adjusting the temperature range and adapting to ultrasonic functions, the cross-linking quality of the core layer is optimized and the temperature of the outer layer is controlled. The first stage heats the core layer to 180℃-200℃, a temperature range that coincides with the activity peak of the vulcanization accelerator TMTD, enabling rapid initiation of the rubber molecular chain cross-linking reaction. Ultrasonic vibration accelerates molecular chain diffusion and collision, reducing the inhomogeneity of the cross-linking network and improving the structural consistency of the core layer. Simultaneously, the low-melting-point phase change material in the second composite layer undergoes a phase change at this temperature, efficiently absorbing excess heat transferred from the core layer, strictly limiting the outer layer temperature to 110℃-130℃. This temperature only triggers the pre-vulcanization of the outer rubber, avoiding gradient failure caused by simultaneous cross-linking of the outer and core layers. The thermotropic shape memory polymer maintains its initial morphology at this temperature, preventing preform structural distortion. The second stage involves maintaining the core layer at a temperature of 190℃-205℃, which is sufficient to consolidate the cross-linking reaction without exceeding the thermal stability range of EPDM rubber. The ultrasonic power is increased to 1000W, and the stronger vibration energy can eliminate the minor defects formed in the early cross-linking stage, further densifying the cross-linking network and ensuring that the core layer achieves excellent mechanical properties and structural stability.

[0040] Example 7, Step 4, to complete the full vulcanization includes the following steps: Step 41: The sealing strip enters the zoned temperature-controlled hot air vulcanizing box. The front hot air temperature is 200℃-220℃. At the same time, the directional infrared energy replenishment device is turned on. Based on the monitoring data of the near-infrared spectroscopy monitor in Step 2, infrared energy with an energy density of 100W / cm²-150W / cm² is output to the corners. Step 42: The high-melting-point phase change material and the first composite layer of the electro-induced shape memory polymer undergo a phase change, absorbing heat to stabilize the surface temperature at 190℃-210℃. The electro-induced shape memory polymer maintains the vulcanization required shape under the action of temperature, avoiding deformation. Step 43: The sealing strip enters the rear hot air zone, and the hot air temperature is adjusted to 180℃-190℃. The temperature is maintained for 5-8 seconds. The first composite layer and the second composite layer release the latent heat of phase change simultaneously, which continuously provides stable heat for the cross-linking reaction of the functional outer layer, ensuring that the cross-linking degree of the functional outer layer reaches more than 85%.

[0041] In Example 8, the formula for calculating the directional energy replenishment density in step 41 is: Es = Et − Eh × ηg × ηmks; Where Es is the directional energy replenishment energy density, Et is the target vulcanization energy density, which is determined by the energy per unit area required for the functional outer layer to achieve 85% crosslinking degree, Eh is the effective energy density of hot air, ηg is the edge and corner geometric correction coefficient, ηm is the material distribution uniformity coefficient, and ks is the safety factor.

[0042] By adopting the above technical solution, a two-layer energy supply system of basic energy and targeted energy replenishment is constructed to solve the problem of insufficient energy for vulcanization at the edges and corners. The front-end hot air provides the basic energy required for the outer layer of vulcanization, meeting the energy needs of most areas. However, due to geometric limitations, the energy reception efficiency of hot air in the edges and corners is lower than that in the main area, easily leading to a vulcanization energy gap. Monitoring data from a near-infrared spectroscopy detector can accurately reflect the uniformity of material distribution in the edges and corners, providing a basis for judging energy replenishment needs.

[0043] The calculation formula in Example 8 achieves accurate calculation of energy replenishment density by quantifying key parameters: the target vulcanization energy density clarifies the energy standard for the outer layer to reach the set degree of crosslinking, the effective energy density of hot air quantifies the actual contribution of hot air, the edge geometry correction coefficient and the material distribution uniformity coefficient compensate for the differences in energy loss caused by the geometry and material distribution, respectively, and the safety factor ensures the sufficiency of energy transfer during the energy replenishment process. In the end, the directional infrared energy replenishment satisfies the edge energy gap without exceeding the material tolerance range, thus achieving targeted and precise energy replenishment.

[0044] Step 42 utilizes the characteristics of the first composite layer to achieve dual stable control of temperature and morphology. The phase transition temperature of the high-melting-point phase change material matches the target vulcanization temperature of the outer layer. Under the combined action of hot air and infrared supplementary energy, a phase transition occurs, absorbing a large amount of excess heat and stabilizing the surface temperature of the functional outer layer within a suitable vulcanization range. This avoids local overheating leading to material degradation or insufficient temperature affecting the crosslinking reaction. The electro-induced shape memory polymer maintains its preset shape under this temperature environment, effectively constraining the stretching, shrinkage, or deformation of the functional outer layer during vulcanization, ensuring the integrity of the product structure during vulcanization, and creating a morphological basis for uniform crosslinking.

[0045] Step 43 works by synergistically combining heat preservation and latent heat release to ensure a complete cross-linking reaction. The temperature of the subsequent hot air is lowered to the heat preservation zone to prevent excessive vulcanization caused by sustained high temperatures, while simultaneously providing a stable environment for the cross-linking reaction. The first and second composite layers simultaneously release the latent heat of phase change stored earlier, forming a continuous and stable heat supply. This compensates for any potential heat loss during the hot air heat preservation stage, providing continuous energy support for the full cross-linking of the functional outer layer's rubber molecular chains. This ensures that the degree of cross-linking reaches the set standard, achieving the required mechanical and sealing properties of the functional outer layer.

[0046] In Example 9, in step 5, the cooling tunnel is divided into three sections, which respectively use 10°C ethylene glycol solution, 25°C deionized water, and 40°C air as cooling media to form a temperature gradient; The spray system adopts a pulse mode of 15 seconds of spraying and 10 seconds of stopping, with a spray pressure of 0.3MPa-0.5MPa; A temperature sensor is installed at the cooling end. When the temperature of the sealing strip drops to 80℃, a weak electric field of 10kV / m-20kV / m is turned on to trigger the shape recovery of the electro-induced shape memory polymer.

[0047] By adopting the above technical solution, the principle of gradient cooling is to use a cooling medium with gradually increasing temperature to weaken the internal stress caused by temperature difference. The three sections of the cooling tunnel use 10℃ ethylene glycol solution, 25℃ deionized water, and 40℃ air respectively, forming a temperature gradient from low to high. The first section, ethylene glycol solution, with its good thermal conductivity and low freezing point, quickly removes a large amount of heat from the surface of the sealing strip, initially reducing the core temperature; the second section, deionized water, serves as a transition medium to alleviate the stress impact caused by the sudden temperature drop; the third section, air, achieves slow cooling, allowing the internal and surface temperatures of the sealing strip to gradually converge. This progressive cooling mode avoids the problem of excessive internal and external temperature differences caused by traditional single low-temperature cooling, reduces internal stress concentration, protects the cross-linked network structure formed after vulcanization from damage, and reduces the risk of deformation.

[0048] The principle behind pulse spray mode is to balance cooling efficiency and temperature uniformity. During the 15-second spray phase, high-pressure water mist directly contacts the sealing strip, efficiently conducting heat and rapidly reducing surface temperature. The 10-second stop-spray phase allows time for internal heat to transfer outwards, and, combined with the latent heat of phase change released by the first and second composite layers, smooths out temperature differences across the cross-section, preventing localized overcooling or heat accumulation. The spray pressure of 0.3MPa-0.5MPa is precisely calibrated to ensure uniform water mist coverage and stable cooling effect, while preventing excessive pressure from impacting the sealing strip structure and causing surface damage or morphological distortion.

[0049] The principle of weak electric field triggering utilizes the electric field response characteristics of electro-induced shape memory polymers to achieve precise shape correction. When the cooling end temperature drops to 80℃, the sealing strip has initially solidified but still retains a certain degree of plasticity. At this point, a weak electric field of 10kV / m-20kV / m is applied. This electric field strength is precisely matched with the conductivity and temperature state of the electro-induced shape memory polymer, effectively triggering its molecular chain reconstruction and restoring the preset ideal shape. This process can correct minor dimensional deviations that may occur during the cooling stage, further improving the straightness and dimensional accuracy of the sealing strip, ensuring its installation compatibility and sealing performance meet standards.

[0050] Example 10: The final product has a tensile strength greater than or equal to 15 MPa, an elongation at break greater than or equal to 400%, a sealing pressure deviation less than or equal to ±0.02 MPa, and a straightness error less than or equal to 0.1 mm / m.

[0051] The following specific embodiments illustrate the implementation principle of the present invention: The functional outer layer is a blend of EPDM and PER lubricant at a mass ratio of 95:5; the core layer containing the sensing medium is EPDM rubber mixed with 6wt% nano-soft magnetic ferrite particles and 0.4wt% vulcanization accelerator TMTD; the functional inner layer is a composite of EPDM and nanofibers at a mass ratio of 94:6. The high-melting-point phase change material has a phase change temperature of 200℃, and the low-melting-point phase change material has a phase change temperature of 155℃; the electro-induced shape memory polymer contains 3.0wt% conductive carbon black, and the thermo-induced shape memory polymer has a glass transition temperature of 165℃. The multilayer structure, from the outside to the inside, consists of the functional outer layer, the first composite layer of high-melting-point phase change material and electro-induced shape memory polymer, the second composite layer of low-melting-point phase change material and thermo-induced shape memory polymer, the core layer containing the sensing medium, and the functional inner layer. It is co-extruded using a variable cross-section composite extruder, with the thickness deviation of each layer controlled within ±0.02mm.

[0052] Pretreatment and shaping parameters: The extruded multi-layered preform first enters a 30kHz ultrasonic pretreatment device with an ultrasonic power set to 650W and a treatment time of 4s, dispersing the agglomerated magnetic media particles through cavitation. It then enters a 10℃ ethylene glycol aqueous solution cooling bath for shaping, with a cooling time controlled at 12s, rapidly fixing the multi-layered structure. The preform after ultrasonic pretreatment is then monitored by both a dielectric constant scanner and a near-infrared spectroscopy detector. A dielectric constant fluctuation ≤2% is considered acceptable, and the uniformity of the shape memory polymer and phase change material dispersion ≥90% is also considered acceptable. Preforms meeting both criteria proceed to subsequent processes.

[0053] Core layer pilot vulcanization parameters: A segmented mid-frequency induction and ultrasonic composite device is used. The first segment uses 25kHz mid-frequency induction and 20kHz ultrasound in synergy, with an ultrasonic power of 500W, to raise the temperature of the core layer containing the induction medium to 190℃. Ultrasonic vibration accelerates molecular chain movement and improves the uniformity of the crosslinking reaction. The second composite layer absorbs heat, maintaining the outer layer temperature at 120℃, and the thermotropic shape memory polymer retains its initial shape. The second segment uses 120kHz mid-frequency induction and 30kHz ultrasound in synergy, increasing the ultrasonic power to 1000W, and maintaining the core layer temperature at 200℃ to eliminate crosslinking network defects and ensure high-quality pilot vulcanization of the core layer.

[0054] The functional outer layer is fully vulcanized using the following parameters: The sealing strip enters the zoned temperature-controlled hot air vulcanization chamber, with the front hot air temperature set at 210℃. Simultaneously, the directional infrared energy replenishment device is activated. Based on the near-infrared spectroscopy data from step 2, and combined with the directional energy replenishment density calculation formula, the energy replenishment requirement is calculated. The target vulcanization energy density Et is 300W / cm², the effective hot air energy density Eh is 175W / cm², the corner geometric correction coefficient ηg is 0.75, the material distribution uniformity coefficient ηm is 0.85, and the safety factor ks is 0.93. The calculated Es is approximately 202.6W / cm², exceeding the set range. Therefore, a final directional output of 150W / cm² infrared energy is used to replenish the corner areas. The first composite layer undergoes a phase transition, absorbing heat to stabilize the surface temperature of the functional outer layer at 200℃. The electro-induced shape memory polymer maintains the required vulcanization shape. Subsequently, the sealing strip enters the rear hot air zone, the hot air temperature is adjusted to 185℃, and it is kept warm for 6 seconds. The first composite layer and the second composite layer release the latent heat of phase change simultaneously, which continuously provides stable heat for the cross-linking reaction of the functional outer layer, ensuring that the cross-linking degree of the functional outer layer reaches more than 85%.

[0055] Gradient cooling parameters: The cooling tunnel is divided into three sections, using 10℃ ethylene glycol solution, 25℃ deionized water, and 40℃ air as cooling media to create a temperature gradient. The spray system uses a pulse mode of 15 seconds of spraying and 10 seconds of stopping, with the spray pressure set at 0.4MPa. A temperature sensor is installed at the cooling end; when the temperature of the sealing strip drops to 80℃, a weak electric field of 15kV / m is activated to trigger the shape recovery of the electro-induced shape memory polymer.

[0056] Post-processing and shaping parameters: The cooled sealing strip is placed in a 175℃ constant temperature shaping chamber and kept at that temperature for 4 minutes. Then, it is cooled to room temperature at a cooling rate of 5℃ / min to fix the shape memory polymer into its final shape.

[0057] Product performance test results: The final automotive rubber sealing strip tested showed a tensile strength of 16 MPa, an elongation at break of 420%, a sealing pressure deviation of ±0.015 MPa, and a straightness error of 0.08 mm / m. All performance indicators met the preset requirements.

[0058] Table 1 shows the performance comparison results between this solution and the traditional solution: Table 1

[0059] The typical values ​​of the traditional solution are based on the product performance statistics of the industry's conventional overall synchronous vulcanization and single cooling process. In the performance change, the improvement refers to the performance optimization of this solution relative to the traditional solution, and the decrease refers to the reduction of error or deviation of this solution relative to the traditional solution.

[0060] The preferred embodiments of the invention are not intended to limit the scope of protection of the invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the invention should be covered within the scope of protection of the invention.

Claims

1. A method for the gradient vulcanization of rubber sealing strips for automobiles, characterized in that, The method comprises the following steps: Step 1: a multi-layer structure embryo is formed by variable cross-section composite extrusion head co-extrusion, the multi-layer structure embryo comprises a functional outer layer, a first composite layer of high-melting-point phase change material and electro-type shape memory polymer, a second composite layer of low-melting-point phase change material and thermo-type shape memory polymer, a core layer containing an inductive medium, and a functional inner layer; Step 2: the multi-layer structure embryo is pre-treated by ultrasonic, and is shaped by a 5-15℃ cooling tank; Step 3: the core layer containing the inductive medium is heated to 180-205℃ and the pilot vulcanization is completed by the synergistic effect of medium-frequency induction and ultrasonic through a segmented medium-frequency induction ultrasonic composite device, and the temperature of other layers is maintained at 110-130℃; Step 4: the functional outer layer is fully vulcanized by temperature control of the electro-type shape memory polymer composite layer under the action of 200-220℃ front hot air and 180-190℃ rear hot air combined with directional infrared energy supplement; Step 5: the sealing strip is gradually cooled by passing through a cooling tunnel, and sequentially passing through a first gradient temperature glycol solution, a second gradient temperature deionized water and a third gradient temperature air for gradient cooling, and is matched with pulse mode spraying and stopping spraying; Step 6: the sealing strip is kept in a 170-180℃ constant temperature shaping box for 3-5 min, and then is cooled to room temperature at a set cooling rate, so that the shape memory polymer is fixed in the final shape.

2. The method for producing a rubber seal strip for an automobile by gradient vulcanization according to claim 1, characterized by, The core layer containing the inductive medium in step 1 is EPDM rubber mixed with 5wt%-8wt% nano soft magnetic ferrite particles and 0.3wt%-0.5wt% vulcanization accelerator TMTD, the functional outer layer is a blended layer of EPDM and PER slip material, and the functional inner layer is a composite layer of EPDM and nano fibers; The phase change temperature of the high-melting-point phase change material is 190-210℃, the phase change temperature of the low-melting-point phase change material is 150-160℃, the electro-type shape memory polymer contains 2.8wt%-3.1wt% conductive carbon black, and the glass transition temperature of the thermo-type shape memory polymer is 160-170℃.

3. The method for producing a rubber seal strip for an automobile by gradient vulcanization according to claim 2, characterized by, In step 2, the extruded multi-layer structure embryo is first subjected to ultrasonic pretreatment by a 20-40kHz ultrasonic pretreatment device with an ultrasonic power of 500-800W to disperse the agglomerated magnetic medium particles by cavitation effect for 3-5s, and then is shaped in a 5-15℃ glycol aqueous solution cooling tank for 10-15s.

4. The method for producing a gradient-vulcanized rubber seal strip for an automobile according to claim 3, characterized by, In step 2, the ultrasonic pretreated blank is sequentially detected by a mechanical energy dielectric constant scanner and a near-infrared spectrum detector, the dielectric constant fluctuation monitored by the dielectric constant scanner is less than or equal to a set fluctuation threshold value to be qualified, and the near-infrared spectrum judges the dispersion uniformity of the shape memory polymer and the phase change material by characteristic peak intensity, the dispersion uniformity is greater than or equal to a uniformity threshold value to be qualified, and the blank is subjected to step 3 after the dielectric constant fluctuation and the dispersion uniformity are both qualified.

5. The method for producing a rubber seal strip for an automobile by gradient vulcanization according to claim 4, characterized by, In step 3, the first section of the segmented medium-frequency induction ultrasonic composite device adopts 10-50kHz medium-frequency induction and 20kHz ultrasonic synergy, the second section adopts 50-200kHz medium-frequency induction and 30kHz ultrasonic synergy, and the ultrasonic power is 500-1000W.

6. The method of claim 5, wherein the gradient vulcanization is performed by using a plurality of heating zones. The first core layer of the frequency induction ultrasonic composite device in step 3 is heated to 180-200 DEG C, and the ultrasonic vibration accelerates the molecular chain movement to improve the uniformity of the crosslinking reaction; the second composite layer absorbs heat, and the outer layer temperature is maintained at 110-130 DEG C, and the shape memory polymer maintains the initial shape; The second core layer is kept at 190-205 DEG C, and the ultrasonic power is increased to 1000W to eliminate the defects of the crosslinking network.

7. The method for producing a gradient-vulcanized rubber seal strip for an automobile according to claim 6, characterized by, Step 4 completes the full vulcanization, including the following steps: Step 41, the sealing strip enters the partition temperature control hot air vulcanization box, the front section hot air temperature is 200-220 DEG C, and the directional infrared energy supplementing device is started at the same time, based on the monitoring data of the near-infrared spectrum monitor in step 2, the infrared energy with an energy density of 100-150 W / cm2 is output to the edge and corner parts; Step 42, the high-melting-point phase change material and the first composite layer of the electrotype shape memory polymer undergo phase change, absorb heat to stabilize the surface temperature at 190-210 DEG C, and the electrotype shape memory polymer maintains the required shape for vulcanization under the action of temperature, avoiding deformation; Step 43, the sealing strip enters the rear hot air zone, the hot air temperature is adjusted to 180-190 DEG C, and the temperature is kept for 5-8s, the first composite layer and the second composite layer release latent heat of phase change at the same time, which provides stable heat for the crosslinking reaction of the functional outer layer, and ensures that the crosslinking degree of the functional outer layer reaches more than 85%.

8. The method for producing a gradient-vulcanized rubber seal strip for an automobile according to claim 7, characterized by, The calculation formula of the directional energy supplementing density in step 41 is: ； wherein is the directed supplemental energy density, is the target vulcanization energy density determined by the energy per unit area required to achieve 85% crosslinking by the functional outer layer, is the hot air effective energy density, is the corner geometry correction factor, is the material distribution uniformity factor, is the safety factor.

9. The gradient vulcanization preparation method for automotive rubber sealing strips according to claim 8, characterized in that, In step 5, the cooling tunnel is divided into three sections, which respectively use 10 DEG C ethylene glycol solution, 25 DEG C deionized water and 40 DEG C air as cooling medium to form a temperature gradient; The spray system adopts a pulse mode of 15s spraying and 10s stopping, and the spray pressure is 0.3-0.5 MPa; A temperature sensor is arranged at the end of the cooling tunnel, and when the temperature of the sealing strip drops to 80 DEG C, a weak electric field with a strength of 10-20 kV / m is started to trigger the shape recovery of the electrotype shape memory polymer.

10. The gradient vulcanization preparation method for automotive rubber sealing strips according to claim 9, characterized in that, The tensile strength of the final product is greater than or equal to 15 MPa, the elongation at break is greater than or equal to 400%, the sealing pressure deviation is less than or equal to ±0.02 MPa, and the straightness error is less than or equal to 0.1 mm / m.

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