Anti-aging sealing gasket and manufacturing method thereof

Abstract

The invention belongs to the technical field of shield tunnel sealing, and particularly relates to an anti-aging sealing gasket and a manufacturing method thereof.The anti-aging sealing gasket comprises a sealing gasket base material and a coating sprayed on the base material, and the coating comprises a first coating and a second coating which are sequentially sprayed on the base material. The manufacturing method of the anti-aging sealing gasket comprises the steps of base material pretreatment, two coating blending, coating spraying and the like, coating blending comprises first coating blending, second coating blending, viscosity testing and the like, so that the viscosity of the coating meets the working requirement, and the coating can be better adhered to the base material. The anti-aging EPDM sealing gasket has good macroscopic physical and mechanical properties in the thermal oxidation aging process, the increase speed of hardness and density is slow, the performance retentivity is high, and the compression set is small. The results show that the anti-aging EPDM sealing gasket has better anti-aging and elastic degradation performance, and the effectiveness of the coating on the aspect of improving the durability and the elasticity of the EPDM sealing gasket is highlighted.

Description

Technical Field

[0001] The present invention relates to the technical field of shield tunnel sealing, and in particular to an anti-aging sealing gasket and a manufacturing method thereof. Background Art

[0002] EPDM gaskets, as the basic waterproofing components of shield tunnel waterproofing systems, directly affect the overall service life and operational safety of the tunnel. In a complex environment characterized by high water pressure and long-term drastic temperature fluctuations, EPDM gaskets are susceptible to mechanical forces and oxygen, leading to aging and stress relaxation. The aging mechanism of EPDM gaskets involves molecular chain breakage and cross-linking, resulting in reduced elasticity. In shield tunnels, thermal oxidative aging driven by oxygen exposure and temperature fluctuations is the main cause of EPDM gasket degradation. In a thermal oxidative environment, molecular chains break to produce free radicals, triggering a series of oxidation reactions, including initiation, propagation, and termination stages. These free radical reactions produce non-free radical products, which reduce the elastic properties of the rubber. In the thermal oxidative aging process, oxygen acts as both an initiator and a reactant, while heat accelerates these reactions and aggravates molecular damage.

[0003] Existing research shows that by introducing oxidants and antioxidants, the heat-oxidative aging resistance of EPDM rubber can be significantly improved while maintaining its mechanical properties. In addition, the use of a specific ratio of carbon black, sulfur, polyethylene glycol and zinc oxide (120:2:3:5) can further optimize its anti-aging properties. Although antioxidants have shown excellent anti-aging properties, existing materials still have defects in anti-aging performance and cannot meet the high requirements of tunnel engineering for the long-term durability of sealing gaskets. Current methods for improving sealing gaskets mainly involve incorporating antioxidants into the rubber matrix to enhance heat resistance and oxygen aging performance. However, these internal modification methods face challenges such as uneven distribution of additives and limited effectiveness under harsh environmental conditions. Summary of the Invention

[0004] The present invention addresses the above-mentioned issues and provides an anti-aging gasket and a method for its manufacture. A polymer coating forms a protective layer on the surface of an EPDM gasket, isolating it from oxygen and mitigating oxidative aging. The effect of the coating encapsulation method on the aging performance of EPDM gaskets used in shield tunnel segment joints was also evaluated. The performance differences between conventional and anti-aging EPDM gaskets were compared using macroscopic, microscopic, and molecular testing and life prediction models, demonstrating the effectiveness of this method in improving gasket durability and extending service life.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: An anti-aging sealing gasket includes a sealing gasket substrate and a coating sprayed on the substrate, wherein the coating includes a first coating and a second coating sprayed on the substrate in sequence, the first coating has a thickness of 1 mm, and the second coating has a thickness of 1 mm.

[0006] Preferably, in the present invention, the first coating layer is a S06-N-1 polyurethane thick film primer layer, and the second coating layer is a S04-60 acrylic polyurethane semi-gloss magnetic paint layer.

[0007] A method for manufacturing the anti-aging sealing gasket comprises the following steps: (1) Substrate pretreatment: polish and clean the substrate surface to increase the surface roughness of the substrate; (2) Paint preparation: S1: Preparing the first coating: Accurately weigh an appropriate amount of the first coating base, place it in a clean, dry container that is easy to stir, add a curing agent and a diluent to the first coating base, and stir to obtain the first coating; S2: Prepare the second coating: Accurately weigh an appropriate amount of the second coating base, place it in a clean container that is easy to stir, add a curing agent and a diluent to the second coating base, and stir to obtain the second coating; S3: Viscosity test: Test the viscosity of the first coating and the second coating respectively. If the viscosity does not meet the working requirements, adjust the coating to a suitable working viscosity by adding an appropriate amount of diluent; (3) Coating spraying: The first coating is evenly sprayed on the pre-treated substrate surface. After spraying, the workpiece is dried. The main purpose of the drying step is to allow the coating to initially solidify at a relatively low temperature, remove moisture from the coating, and form a solid structure on the coating surface. The dried workpiece is then placed in a baking environment at 30-35°C for 1.5-2 hours to obtain the first coating. After cooling, the second coating is evenly sprayed on the first coating under the same spraying conditions. After spraying, the workpiece is dried and baked in the same manner to obtain the anti-aging sealing gasket.

[0008] In the present invention, preferably, the mass ratio of the first coating main agent to the curing agent is 100:10-15; the mass ratio of the second coating main agent to the curing agent is 100:20-25.

[0009] In the present invention, preferably, the stirring time in step S1 is 5-15 minutes, and the stirring speed is 500-1000 rpm.

[0010] In the present invention, preferably, the first coating main agent is S06-N-1 polyurethane thick film primer, and the second coating main agent is S04-60 acrylic polyurethane semi-gloss magnetic paint.

[0011] In the present invention, preferably, the spraying is to transfer the first coating or the second coating with adjusted viscosity to a spraying device for spraying, the spraying pressure is 0.2-0.5 MPa, the spraying distance is 20-40 cm, and the spraying angle is 45-90 degrees.

[0012] In the present invention, preferably, the curing agent is G-1 curing agent (hydroxyethylethylenediamine), and the diluent is X-11 polyurethane paint diluent.

[0013] In the present invention, preferably, in step S2, after adding the curing agent and the diluent, the prepared coating is polished with 100# sandpaper and then stirred.

[0014] In the present invention, preferably, the working viscosity in step S3 is 0.00135-0.00225 Pa·s.

[0015] By adopting the above technical solution, the beneficial effects of the present invention are: (1) The performance of the anti-aging EPDM gasket during the thermal oxidative aging process was superior to that of the conventional EPDM gasket, with a slower increase in hardness and density, higher performance retention, and smaller compression set. These results indicate that the anti-aging EPDM gasket has better resistance to aging and elastic degradation, highlighting the effectiveness of spray-on anti-aging coatings in improving the long-term durability and elasticity of EPDM gaskets.

[0016] (2) Based on the time-temperature superposition principle and life prediction model, spraying the anti-aging coating of the present invention can significantly extend the estimated service life of anti-aging EPDM gaskets. After 100 years of use, the stress retention rate of the anti-aging gasket of the present invention (0.536) is higher than that of conventional gaskets (0.458).

[0017] (3) From a molecular perspective, the anti-aging treatment of the present invention reduces the changes in the functional groups of the EPDM gasket, thereby reducing the aging of the material. This is manifested in a decrease in the storage modulus, loss modulus, and glass transition temperature, which indicates that the cross-linking density and stiffness of the anti-aging EPDM gasket are lower than those of conventional EPDM gaskets, and that the anti-aging EPDM gasket has less energy loss due to viscous deformation during deformation, and the viscosity of the material is reduced, thereby reducing the energy loss during stress. FTIR analysis further verified the chemical structure stability of the anti-aging EPDM gasket, with minimal fluctuation in the characteristic peak amplitude and fewer bonds formed or consumed during aging. Thermogravimetric analysis showed that the anti-aging EPDM gasket had better thermal stability and quality retention than conventional EPDM gaskets, indicating the protective effect of this method.

[0018] (4) At the microstructural level, the surface morphology of the EPDM gasket gradually changed with increasing aging time. Cracks and micropores formed in the initial stage, interconnected voids and delamination appeared in the middle stage, and macropores and obvious delamination formed in the final stage. Compared with traditional EPDM gaskets, the anti-aging EPDM gasket had better structural integrity throughout the aging process, with fewer cracks, smaller voids, and less delamination.

[0019] Furthermore, after coating application, the present invention first performs a drying process for preliminary curing, followed by baking to accelerate complete curing. This not only avoids surface defects such as bubbles and cracks (i.e., staged curing prevents surface defects caused by instantaneous solvent volatilization at high temperatures), but also ensures coating uniformity: the initially cured coating does not readily flow during baking, ensuring a uniform spray thickness and avoiding edge sagging. Furthermore, the stable curing process enhances the coating's aging resistance, thereby extending the gasket's service life in harsh environments (such as high water pressure and temperature fluctuations). Therefore, the combination of drying and baking balances production efficiency and coating quality, while enabling precise control of material properties through scientific temperature control. This process is particularly suitable for sealing components with high durability requirements (such as shield tunnel gaskets), significantly reducing maintenance costs and safety hazards caused by coating failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of rubber sealing gasket in shield tunnel.

[0021] Figure 2 The figure is a flow chart of the spray packaging process of the anti-aging sealing gasket of the present invention.

[0022] Figure 3 Analysis diagram of the macro-mechanical properties (a: hardness, b: density, c: performance retention, d: compression permanent deformation) of conventional and anti-aging sealing gaskets during thermal oxidation aging.

[0023] Figure 4 The microstructure diagrams of conventional EPDM gaskets and anti-aging EPDM gaskets at different aging times.

[0024] Figure 5 The figure shows a comparison of the microstructure and performance retention rate of conventional EPDM gaskets and anti-aging EPDM gaskets at different aging times.

[0025] Figure 6 Analysis diagram of G' at different aging times: (a) conventional EPDM; (b) anti-aging EPDM.

[0026] Figure 7 Analysis diagram of G'' under different aging times: (a) conventional EPDM; (b) anti-aging EPDM.

[0027] Figure 8 Loss factor analysis diagram under different aging times: (a) conventional EPDM; (b) anti-aging EPDM.

[0028] Figure 9 This is a DMA comparison chart of conventional EPDM and anti-aging EPDM under aging time of 168 hours.

[0029] Figure 10 This is a comparison of the cross-linking density of conventional EPDM gaskets and anti-aging EPDM gaskets.

[0030] Figure 11 FTIR of different aging times: (a) EPDM gasket; (b) anti-aging EPDM gasket.

[0031] Figure 12 This is a FTIR comparison chart of conventional EPDM and anti-aging EPDM after aging time of 168 hours.

[0032] Figure 13 This is a comparison chart of the mass fraction and mass change rate of conventional EPDM sealing gaskets and anti-aging EPDM sealing gaskets.

[0033] Figure 14 The fitting curves and relationship equations of experimental data at different temperatures: (a) conventional EPDM sealing gasket; (b) anti-aging EPDM sealing gasket.

[0034] Figure 15 Figure 3. The relationship between linear fitting and translation factor at different temperatures: (a) conventional EPDM gasket; (b) anti-aging EPDM gasket.

[0035] Figure 16 Natural aging curves under 12 mm compression: (a) conventional EPDM gasket; (b) anti-aging EPDM gasket.

[0036] Figure 17 Cooperative deformation diagrams of EPDM and coating at different compression levels: (a) 0 mm; (b) 3 mm; (c) 6 mm; (d) 9 mm. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example 1

[0038] An anti-aging sealing gasket comprises a sealing gasket substrate and a coating sprayed onto the substrate. The coating comprises a first coating layer and a second coating layer sprayed sequentially onto the substrate. The first coating layer has a thickness of 1 mm, and the second coating layer has a thickness of 1 mm. In this embodiment, the first coating layer is a S06-N-1 polyurethane thick-film primer layer, and the second coating layer is a S04-60 acrylic polyurethane semi-gloss magnetic paint (topcoat) layer. The substrate used in this embodiment is EPDM (ethylene propylene diene monomer) rubber.

[0039] The method for manufacturing the above-mentioned anti-aging sealing gasket comprises the following steps: Step 1: Substrate preparation and treatment 1. Prepare materials such as EPDM (ethylene propylene diene monomer) substrate, S06-N-1 coating (main agent, S06-N-1 polyurethane thick-film primer), S04-60 coating (main agent, S04-60 acrylic polyurethane semi-gloss magnetic paint), G-1 curing agent (hydroxyethyl ethylenediamine), X-11 thinner, and 100# sandpaper. Also prepare grinding tools, mixing equipment, spraying equipment, dipping equipment, baking equipment, and viscosity testing equipment.

[0040] 2. Use 100# sandpaper to carefully polish the surface of the EPDM substrate to remove impurities, oil stains, oxide layer, etc. on the surface of the substrate, increase the surface roughness, and improve the adhesion between the coating and the substrate.

[0041] Step 2: Paint mixing To prepare the S06-N-1 coating, weigh 500g of the S06-N-1 coating base and place it in a clean, dry, and easily stirred container. Add 50g of the G-1 curing agent to the S06-N-1 coating base. Also, add a small amount of the X-11 diluent to adjust the coating's viscosity. After addition, use a stirring device to uniformly stir the mixture, adjusting the stirring time and speed appropriately (in this example, the specific stirring time is 10 minutes and the stirring speed is 1000 rpm) to ensure that the curing agent, diluent, and coating base are thoroughly mixed to form a uniform coating system.

[0042] 2. To prepare the S04-60 paint, weigh 500g of S04-60 base and place it in a clean mixing container. Add 110g of G-1 curing agent to the S04-60 base, or a small amount of X-11 thinner, as needed. Add slowly and evenly. Sand the prepared paint briefly with 100# sandpaper. Apply the paint to a smooth surface and then gently sand it to refine the paint particles. Finally, stir the paint again with an electric stirrer for about 10 minutes.

[0043] 3. After stirring, use a viscometer to test the viscosity of S06-N-1 paint and S04-60 paint respectively. If the viscosity does not meet the working requirements, adjust the paint to the appropriate working viscosity (0.00225 Pa·s) by adding an appropriate amount of diluent and further stirring to ensure the smooth progress of the subsequent spraying process.

[0044] Step 3: Paint spraying First, the S06-N-1 coating with adjusted viscosity is transferred to the spraying equipment, and suitable spraying pressure, spraying distance, spraying angle, etc. are selected to ensure that the coating can be evenly sprayed on the pretreated EPDM substrate surface. In the present embodiment, the spraying pressure is 0.5MPa, the spraying distance is 30 cm, and the spraying angle is 60 degrees. After spraying is completed, the workpiece is dried under suitable environmental conditions, and the drying time and environmental conditions need to be strictly controlled according to the drying characteristics and process requirements of the coating to ensure that the coating can be fully dried and solidified to form a stable coating structure. After the coating cools down, it is polished with 100# sandpaper, and then the S04-60 coating is sprayed with the same spraying conditions. After spraying again, the workpiece is placed in a well-ventilated environment to dry. The drying time is determined according to the coating drying characteristics and generally requires 1-2 hours. Finally, the dried workpiece is placed in a baking environment at 30°C and baked for 2 hours. Example 2

[0045] In this embodiment, except for the mass ratio of the curing agent to the coating main agent, which is different from that in Example 1, everything else is the same as that in Example 1.

[0046] In this embodiment, the mass ratio of the S06-N-1 coating base to the G-1 curing agent is 100:12, and the mass ratio of the S04-60 coating base to the G-1 curing agent is 100:20. Example 3

[0047] In this embodiment, except for the mass ratio of the curing agent to the coating main agent, which is different from that in Example 1, everything else is the same as that in Example 1.

[0048] In this embodiment, the mass ratio of the S06-N-1 coating base to the G-1 curing agent is 100:15, and the mass ratio of the S04-60 coating base to the G-1 curing agent is 100:25.

[0049] The applicant also conducted experiments to evaluate the thermal-oxidative aging of the aged EPDM gasket using conventional EPDM gaskets (also referred to as aged EPDM gaskets) and aged EPDM gaskets. The gasket compression was set at 12 mm, equivalent to a 3 mm gap opening. Three different aging temperatures were established for the experiments: 70°C, 85°C, and 100°C. The number of samples is shown in Table 1. The macromechanical properties of the EPDM gaskets were evaluated through density and hardness tests. Samples used for density testing measured 5 mm in length, 4 mm in width, and 2 mm in thickness. At each time point, two samples were tested under all aging conditions, and their average density was calculated. For hardness measurements, 50 mm long strips were used, and hardness values were recorded at five evenly spaced locations on the surface, with 6 mm intervals between each location. Other macromechanical properties, including pressure relaxation and compression set, were evaluated using a WDW-50 electronic universal testing machine. Advanced technology was used to analyze the microstructural and molecular changes in the EPDM gaskets under aging conditions at 100°C and 12 mm compression. After liquid nitrogen embrittlement treatment, the microstructural changes of the prepared samples were observed under 1500x magnification using SEM. FTIR was used to identify molecular structural changes, and DMA was used to examine dynamic mechanical behavior. Furthermore, TG was used to quantify mass loss throughout the aging process, providing a comprehensive understanding of the material's durability.

[0050] Table 1 Thermal oxidation aging test number

[0051] This invention was applied to the analysis of a Chinese subway shield tunnel. The shield tunnel has a burial depth of 15.39m, an outer diameter of 6.2m, and an inner diameter of 5.5m. The tunnel segment width is 1.2m and the thickness is 0.35m. The design water pressure of the shield tunnel segment joints is 0.209MPa. The porous EPDM sealing gasket is used to waterproof the circumferential and longitudinal joints, such as Figure 1 shown.

[0052] When the joint gap varies from 3.0mm to 10.0mm, the sealing gasket must maintain waterproof integrity. The test sample length is 100mm, and the sample hardness is between 70-75HA. Its specific basic performance indicators are detailed in Table 2.

[0053] Table 2 Basic performance indicators of EPDM seals used in the test

[0054] EPDM gaskets were treated with S06-N-1 polyurethane thick-build primer and S04-60 acrylic polyurethane semi-gloss magnetic coating. Before spray coating, the EPDM gasket surface must be carefully sanded with 100# sandpaper to remove impurities, oil, and oxide layers, increasing surface roughness and improving adhesion between the coating and the substrate. After sanding, the substrate should be thoroughly cleaned and clear of dust, debris, and other residual materials. S06-N-1 polyurethane thick-build primer and G-1 curing agent were then mixed in a precise ratio of 100:10, with X-11 thinner added as needed to adjust viscosity. The primer was then evenly applied to the EPDM gasket surface. A topcoat (S04-60 acrylic polyurethane semi-gloss magnetic paint) was then evenly applied over the primer. The spray coating procedure for the topcoat (S04-60 acrylic polyurethane semi-gloss magnetic paint) is identical to that for the primer. Throughout the entire process, protective gear must be worn and adequate ventilation must be ensured to avoid inhaling dust and paint fumes. Adhering to the specified drying and baking time and temperature requirements is crucial to preventing any encapsulation defects. In this experiment, the coated EPDM gasket is referred to as an anti-aging EPDM gasket. The entire encapsulation process is shown in Figure 2.

[0055] During testing, a durometer, density meter, WDW-50 electronic universal material testing machine, and thickness gauge were used to analyze the hardness, density, performance retention, and compression set of both conventional and anti-aging EPDM gaskets. An SU8010 field emission SEM, Nicolet iS50 FT-IR, DMA, and TG were used to analyze the microstructure, infrared spectroscopy, dynamic mechanical properties, and thermal gravimetric analysis of the two EPDM gaskets.

[0056] The test results are as follows: Figure 3 The macroscopic physical and mechanical properties of conventional and anti-aging EPDM sealing gaskets during thermal oxidation aging are described. Figure 3 It can be seen that at the same aging temperature, the hardness and density of the gasket increase with the increase of aging time. A rapid increase is observed in the early stage. As the aging progresses, the hardness and density increase more slowly and more steadily. At the same aging time, higher aging temperature leads to an increase in hardness and density. It is worth noting that under the same conditions, the hardness and density of the anti-aging EPDM increase less than that of the conventional EPDM (such as Figure 3 (a) and (b) in the figure), highlighting the advantages of anti-aging and elasticity.

[0057] like Figure 3As shown in (c), the performance retention (stress retention) of both gaskets decreases rapidly during the initial aging phase but stabilizes with increasing aging time. At the same aging temperature, performance retention continues to decline over time, while higher temperatures result in even lower retention. At 100°C, the retention of the conventional EPDM gasket decreases from 1 to 0.191, while the aging-resistant EPDM gasket retains a higher value of 0.287. This data demonstrates that the encapsulation process of the aging-resistant EPDM gasket effectively slows the aging process and stabilizes its performance over time.

[0058] like Figure 3 As shown in (d) of Figure 3, the compression set of both gaskets also increases with aging time, rising sharply in the initial stages of aging before gradually stabilizing. Higher aging temperatures exacerbate the deformation, reflecting an accelerated degradation of the gasket's elastic properties. At 100°C, the compression set of conventional EPDM increases from 0 to 80°C, while the increase for the aging-resistant EPDM is smaller, at 77.29°C. These results further confirm the improved durability and stability of the aging-resistant EPDM under the same aging conditions.

[0059] At the same time, the applicant also used SEM to compare the surface morphology of the two gaskets under 100°C and 12mm compression aging conditions. Under the condition of 1500 times magnification, the microstructural changes of the samples after liquid nitrogen embrittlement treatment at different aging stages were observed. The microstructural evolution of conventional EPDM sealing gaskets and anti-aging EPDM sealing gaskets under different aging times is as follows: Figure 4 As shown in Figure 2, the surfaces of both EPDM gaskets appeared relatively smooth and free of cracks when unaged. During the initial aging stage, from 0 to 24 hours, cracks and microvoids appeared on the surface of the conventional EPDM gasket. During this period, the aged EPDM gasket showed minimal damage, exhibiting only surface cracks. This indicates that the anti-aging treatment protected the gasket from initial degradation and preserved its surface integrity. During the intermediate aging stage, from 24 to 96 hours, the cracks and voids within the conventional EPDM gasket gradually expanded. Simultaneously, the surface of the conventional EPDM gasket began to show signs of delamination. During this period, the aged EPDM gasket showed only initial signs of pore formation and the onset of surface precipitation. This indicates that the anti-aging treatment significantly reduced the material degradation rate and maintained the gasket's structural integrity and performance for an extended period. In the final aging stage, after 96 hours, the existing voids and cracks on the surface of the conventional EPDM gasket interconnected to form larger pores. Delamination became increasingly prominent with increasing aging time. At the same time, the amount of pore formation in the anti-aging EPDM gasket increased significantly, and more cracks entered the pores. In summary, the performance of the anti-aging EPDM gasket is significantly better than that of the conventional EPDM gasket.

[0060] like Figure 5 As shown, combining SEM images with performance retention further reveals the physical changes that occur on the surface of EPDM gaskets during aging. The early formation of cracks, the appearance of microvoids in the middle stage, and the development of larger pores and delamination in the later stages all correspond to the observed decrease in performance retention. Anti-aging treatment significantly reduces the extent of surface damage and delays the formation of cracks and voids, which is consistent with the higher performance retention of treated gaskets. Since SEM images show less degradation in the anti-aging EPDM gaskets, the corresponding performance retention values are significantly higher than those of untreated gaskets.

[0061] In addition, the applicant also used molecular analysis (including DMA, infrared spectroscopy and thermogravimetry) to test the performance of the sealing gasket.

[0062] The storage modulus (G') of conventional EPDM sealing gaskets and anti-aging EPDM sealing gaskets changes with aging time as shown in the figure below: Figure 6 As shown. As the temperature increases, the G' of the gasket decreases. Initially, at lower temperatures, the molecular chains within the gasket remain in a glassy state, characterized by high rigidity. As the temperature increases, the sealing gasket approaches its glass transition temperature, and the mobility of these molecular chains increases, causing G' to decrease with increasing temperature. The G' of the sealing gasket remains relatively constant in the early stages of aging, but increases significantly in the middle and late stages. This observation indicates that the stiffness of the sealing gasket is least affected in the early stages of aging, but increases significantly with the passage of aging time. Through comparative analysis of the two EPDM sealing gaskets, it was found that the G' value of the aging-resistant EPDM sealing gasket was lower than that of the conventional EPDM sealing gasket, and the rate of change of the G' value was also reduced. This indicates that the crosslinking density and stiffness of the aging-resistant EPDM sealing gasket are lower than those of the conventional EPDM sealing gasket.

[0063] The loss modulus (G") of conventional EPDM sealing gaskets and anti-aging EPDM sealing gaskets changes with aging time as shown in the figure below: Figure 7As shown. With the increase of temperature, the molecular chain fluidity of EPDM increases, resulting in an increase in the G" value of the sealing gasket, which eventually reaches an initial peak. Subsequently, above a certain temperature threshold, the excessive fluidity of the molecular chain reduces the viscoelasticity of EPDM, resulting in a decrease in G". The trend observed in G" with increasing aging duration indicates that long-term aging can lead to the degradation of the internal cross-linked structure of the gasket, thereby impairing its mechanical properties. Through comparative analysis of the two EPDM sealing gaskets, it was found that the G value of the aging-resistant EPDM sealing gasket was lower than that of the conventional EPDM sealing gasket, and the rate of change of the G" value was also reduced. This finding indicates that the aging-resistant EPDM gasket has less energy loss due to viscous deformation during deformation, and the viscosity of the material is reduced, thereby reducing the energy loss during stress.

[0064] Figure 8 The changes in the loss factor (tan δ) of conventional EPDM gaskets and aging-resistant EPDM gaskets at different aging times are shown. Tg represents the temperature threshold at which a polymer material transitions from a glassy state to a highly elastic state. The Tg of a gasket is determined by the temperature corresponding to the peak of the tan δ curve. Prolonging the aging time of the EPDM gasket will lead to an increase in the Tg value, indicating that the energy required to transition from the glassy state to the elastic state has increased. The increase in the Tg value is also related to the increased rigidity of the gasket's molecular chains. Comparative analysis shows that at the same temperature and aging time, the peak tan δ of the aging-resistant EPDM gasket is smaller than that of the conventional EPDM gasket. This finding indicates that chemical modifications such as molecular chain breakage and cross-linking are relatively less obvious in the aging-resistant EPDM gasket, resulting in a more stable molecular structure.

[0065] like Figure 9 As shown, the aged EPDM gaskets exhibit lower G' values and lower rates of change compared to conventional EPDM gaskets. This phenomenon is attributed to the protective coating's ability to shield the rubber from air exposure, thereby mitigating oxidative degradation, minimizing molecular chain breakage, delaying the aging process, and maintaining the structural integrity of the rubber. In addition, the G" values of the aged EPDM gaskets coated with the protective layer are lower than those of conventional EPDM gaskets. This phenomenon is believed to be due to the coating's effectiveness in reducing internal friction and energy loss in the material, resulting in a decrease in the overall G". In addition, the loss factor of the aged EPDM gasket at Tg is lower than that of the conventional EPDM gasket, indicating a reduced aging effect of the aged variety. It is worth noting that the Tg of the aged EPDM gasket does not show a significant upward trend compared to the conventional EPDM gasket, indicating that the molecular chain stiffness in the aged gasket is still lower. This observation emphasizes the coating's ability to inhibit the aging process of the EPDM gasket.

[0066] Crosslink density is a key parameter in polymer science and can be derived from the storage modulus obtained by DMA. The crosslink density of the two gaskets and the comparison and analysis of their molecular network structures are shown in Figure 2. Figure 10 As shown in Figure 3, as the aging process progresses, the crosslink density shows a clear initial decrease followed by an increase. This phenomenon can be attributed to the oxidation reactions of the rubber material with atmospheric oxygen during the aging process. In the first stage, these oxidation reactions mainly cause the breakage of crosslinks between rubber molecules, resulting in a decrease in crosslink density. However, as aging continues and enters the second stage, new crosslinks gradually form within the rubber, leading to a recovery in crosslink density. It is worth noting that compared with traditional EPDM sealing gaskets, the reduction in crosslink density of the aging-resistant EPDM sealing gasket in the first stage is much smaller. Moreover, during the subsequent aging process in the second stage, the crosslink density of the aging-resistant gasket remains consistently lower than that of conventional EPDM sealing gaskets. This significant difference highlights the superior structural stability of the aging-resistant EPDM sealing gasket. Specifically, the protective coating on the aging-resistant gasket slows down the process of crosslink breakage and reconstruction during thermal oxidative aging, thereby helping to maintain the material's flexibility and sealing effectiveness.

[0067] At the same time, infrared spectroscopy analysis was also performed on conventional EPDM sealing gaskets and anti-aging EPDM sealing gaskets under 100°C and 12 mm compression aging conditions. This analysis aims to identify the organic molecular structure and composition within the gasket. The infrared spectra of the two EPDM sealing gaskets at different aging stages are shown in Figure 2. Figure 11 As shown. With the increase of aging time, 860cm -1 The characteristic peak at 1080cm is enhanced due to the out-of-plane bending vibration of CH. -1 The characteristic peak at 1380cm is enhanced due to the enhanced stretching vibration of the CO bond, indicating that as the aging time increases, oxidation reactions occur and more and more ethers and esters are formed. -1 The characteristic peak at 1520 cm is weakened, indicating that the oxidation reaction consumes some methyl groups, resulting in a decrease in the number of methyl groups. -1 and 1630 cm -1 The significant increase in the peak intensity at 2800 cm is a clear sign of enhanced stretching vibrations of the C=O bond. This indicates that the number of carbonyl groups has increased significantly during aging. The enhancement of these peaks is a direct result of the strengthening of carbonyl bonds, which is a key indicator of the chemical evolution of the material over time. -1 to 3000 cm -1 Peaks in this range are usually associated with CH3, CH2, and CH functional groups. 2920 cm- 1 The peak intensity at 3000 cm-1 gradually increases with aging time, which is mainly due to the enhanced stretching vibration of the -CH2- group.-1 to 3700 cm -1 A broad absorption band appeared in the range of 3640 cm-1, and the intensity of the absorption band became stronger with the increase of EPDM aging time. -1 There is an absorption peak at 10°C, primarily due to the stretching vibration of hydroxyl groups (-OH) under hydrogen bonding. Hydroxyl groups may originate from oxidizing functional groups such as alcohols, hydroperoxides, and carboxylic acids, suggesting an increase in alcohol concentration during aging. Comparing the characteristic peaks of the two EPDM gaskets reveals that the expansion vibration of the aging-resistant EPDM gasket is weaker than that of the standard EPDM gasket. This phenomenon suggests that the coating encapsulates and protects the EPDM gasket during oxidation, thereby reducing the generation of substances.

[0068] The infrared spectrum comparison of conventional EPDM sealing gasket and anti-aging EPDM sealing gasket after aging time of 168h is shown in the figure below. Figure 12 As shown. Under the same aging time, EPDM sealing gasket at 860cm -1 The characteristic peak amplitude fluctuation at 1380 cm is larger than that of the anti-aging EPDM gasket. This indicates that the number of CH bonds generated in the conventional EPDM gasket during the aging process is higher than that of the anti-aging EPDM gasket. In addition, the characteristic peak of conventional EPDM rubber (EPDM) at 1380 cm -1 and 1720cm -1 There are two significant fluctuations at 1380 cm-1, while the characteristic peak of EPDM is only at 1380 cm-1. -1 to 1520cm -1 There are two significant fluctuations. The results show that during the oxidation reaction, the encapsulation slows down the process of EPDM sealing gasket producing methyl and C=O, making the EPDM anti-aging gasket at 1380cm -1 to 1720 cm -1 The fluctuation range between 2920cm -1 and 3640cm -1 The characteristic peaks of the conventional EPDM gasket show greater fluctuations, which means that it produces more CH, alcohol, acid, and other by-products during the oxidation process. In summary, under the same time conditions, the aging degree of the conventional EPDM gasket is higher than that of the anti-aging EPDM gasket.

[0069] As shown in Figure 13, during the thermogravimetric analysis, the mass fraction of the sealing gasket gradually decreased with increasing temperature. Four significant degradations of the EPDM sealing gasket performance were observed throughout the experiment. (1) The initial degradation occurred between 0°C and 200°C, mainly including the evaporation of water and the desorption of adsorbed gases. (2) The second degradation occurred between 200°C and 420°C, characterized by the onset of chemical transformation of the EPDM sealing gasket, mainly through oxidation and cracking reactions of the side chains. During this period, certain functional groups on the rubber molecular chain (C=O, Oh, etc.) became unstable and underwent oxidation reactions, resulting in chain scission and emission of small molecular gases (carbon dioxide, water, etc.). (3) The third degradation occurred between 420°C and 480°C, mainly characterized by the intensification of the EPDM main chain cleavage reaction. As the temperature increased, the CC bonds within the main chain began to break, generating short-chain molecules and free radicals. These entities underwent further recombination, crosslinking, or cracking reactions, ultimately resulting in additional mass loss of the rubber material. (4) The final weight loss occurs between 480℃ and 600℃, indicating that the decomposition of the EPDM gasket is nearly complete, and the residual material is mainly composed of carbonaceous residues. At this critical moment, the process is mainly driven by the continued decomposition of residual organic matter into smaller molecules and subsequent evaporation. Throughout the thermal decomposition process, the mass loss rate of the anti-aging EPDM gasket is lower than that of the conventional EPDM gasket in the early and late stages, while the mass loss rate is higher in some areas of the second and third stages. The reason may be that the non-evaporating gas and side chains of the first and second stage anti-aging EPDM gaskets are completely reacted in the second and third stages. At the same time, the mass loss of the anti-aging EPDM gasket is significantly reduced compared with the conventional EPDM gasket, emphasizing the substantial advantages of the anti-aging EPDM gasket in terms of service life and material stability. Therefore, the anti-aging EPDM gaskets show excellent performance in TG, which indicates that they have the potential to extend the service life in sealing applications.

[0070] The applicant also compared the lifespan predictions to evaluate the effects of aging on material properties using the time-temperature superposition principle. The time-temperature superposition principle is a graphical technique that uses high temperatures to accelerate chemical reactions, allowing for a faster assessment of the effects of aging on material properties.

[0071] Under the influence of thermal oxidative aging, the degradation kinetics of EPDM sealing gasket performance conforms to the Arrhenius model, as shown in formula (1).

[0072] k =Aexp(- E a / R T ) (1) Where k is the reaction rate, A is a constant, Ea is the apparent activation energy, T is the absolute temperature, and R is the gas constant. For a reference temperature T0 at which the reaction rate is k, the scaling factor α of k0 and k0-related T is defined as: α T =exp( E a / R T 0- E a / R T ) (2) Taking the logarithm of both sides of equation (2) with base 10, we can get: lg α T =b(1 / T 0-1 / T ) (3) Where b = (Ea*lge) / R is a constant. Equation (3) shows that αT is linearly related to the inverse of the absolute temperature. First, the critical aging time at each experimental temperature is extrapolated, with the lowest test temperature as the reference (shift factor = 1). The shift factors at other temperatures are calculated based on the critical aging time. The linear relationship between the logarithm of the shift factor and the inverse of the temperature is used to determine the shift factor at ambient temperature. The high-temperature experimental data is then converted to room temperature conditions, and the time degradation pattern of the gasket performance retention rate is fitted. This analysis can predict the gasket's service life at room temperature.

[0073] Using the contact stress relaxation data accumulated during the thermal oxidative aging process, it is possible to predict the service life of a sealing gasket under ambient aging conditions at 23°C. Using the thermal oxidative aging test data of an EPDM sealing gasket compressed to 12mm as an example, the initial contact stress recorded under these conditions was determined to be 2.198 MPa, and the design water pressure was 0.209 MPa.

[0074] Therefore, the dimensionless pressure ratio, denoted as P, is calculated as the ratio of these two values, yielding Ppro = 0.209 / 2.198 = 0.095.

[0075] Origin software was used to perform nonlinear fitting on the two sets of experimental data, and the curves and relationships between P and aging time t at different temperatures were obtained. The correlation coefficient R of each curve exceeded 0.99.

[0076] The performance ratio P pro =0.095Substitute Figure 14 According to the prediction relationship shown, the failure time of conventional EPDM sealing gaskets at different temperatures t can be obtained as follows: t a 70=68859h, t a 85 =8285h, t a 100 =974h. The failure times of anti-aging EPDM gaskets are: t anti 70 =69325h, t anti 85 =10585h, t anti 100 = 2927h. The translation factor at the lower experimental temperature of 70°C was set to 1. Based on the time-temperature superposition principle, the translation factors at 85°C and 100°C were derived and given in Table 3.

[0077] Table 3 Translation factors at different temperatures

[0078] Based on the time-temperature superposition principle, it is deduced that the logarithm of the translation factor at different temperatures is linearly related to the inverse of the absolute temperature T. According to the data in Table 3, the relationship between temperature and translation factor can be obtained by linear fitting using Origin software. The correlation coefficient R of this relationship is greater than 0.99. By substituting the temperature T = 23 ° C (296.15 K) into Figure 15 The established relationship shown above allows the logarithm of the translation factor at this temperature to be calculated. This value is expressed as log(α23). Fitting the experimental data revealed that the logarithms of the translation factors for conventional EPDM gaskets and aging-resistant EPDM gaskets at 23°C were 3.774 and 3.790, respectively. Subsequently, by raising these two values to the power, the translation factors α23 for the two gaskets were determined to be 5942.921 and 6169.440, respectively.

[0079] Using translation factors specific to 85°C and 100°C, the thermal oxidation aging data at these temperatures were recalibrated to simulate conditions at 70°C. Subsequently, the translation factor α was applied to adjust the 7023°C data to align it with the natural aging temperature of 23°C. This method can be used to derive the stress retention rate P and aging time t for the two gaskets under natural aging conditions. At the natural aging temperature, the relationship between the stress retention rate P and the aging time of the conventional EPDM sealing gasket and the anti-aging EPDM sealing gasket is as follows: Figure 16 shown.

[0080] like Figure 16As shown in the figure, the life prediction equations of conventional EPDM sealing gaskets and anti-aging EPDM sealing gaskets when subjected to 12mm compression are as follows: P a = -0.9764*ln(0.04573lnt) (4) P anti =-0.8882*In(0.03983Int) (5) Substituting t = 876000h (equivalent to 100 years) into the above formulas (4) and (5), the stress retention rates under these working conditions are 0.458 and 0.539, respectively. Further calculations show that the contact stress of the conventional sealing gasket after 100 years is 1.007MPa (0.458 × 2.198), and that of the anti-aging EPDM sealing gasket is 1.185MPa (0.539 × 2.198), both exceeding the design water pressure of 0.209MPa and meeting the waterproofing requirements. It is worth noting that the contact stress of the anti-aging EPDM sealing gasket is 0.178MPa higher than that of the conventional EPDM sealing gasket, an increase of approximately 17.6%. The reason why the performance of the anti-aging EPDM sealing gasket only improved by 17.6% is that there is a significant difference between the inherent superelastic properties of the EPDM material and the mechanical properties of the S06-N-1 and S04-60 coatings, as shown in Figure 17.

[0081] The residual contact stress exhibited by the gasket, after a compression of 12 mm over 100 years, exceeds the specified water pressure, fully meeting the century-long waterproofing standard. Furthermore, a lifespan prediction equation shows that after 100 years of exposure to natural conditions, the aging-resistant EPDM gasket maintains better contact stress than conventional EPDM gaskets. Therefore, compared to conventional EPDM gaskets, the aging-resistant EPDM gasket exhibits exceptional aging resistance. Furthermore, the application of a coating has been shown to slow the aging process, thereby extending the service life of EPDM gaskets.

[0082] The above description is a detailed description of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. An anti-aging sealing gasket, characterized in that: The invention comprises a sealing gasket substrate and a coating sprayed on the substrate, wherein the coating comprises a first coating and a second coating sprayed on the substrate in sequence, wherein the thickness of the first coating is 1 mm, and the thickness of the second coating is 1 mm; The first coating layer is a S06-N-1 polyurethane thick film primer layer, and the second coating layer is a S04-60 acrylic polyurethane semi-gloss magnetic paint layer.

2. A method for manufacturing the anti-aging sealing gasket according to claim 1, characterized in that: The steps include: (1) Substrate pretreatment: polish and clean the substrate surface to increase the surface roughness of the substrate; (2) Paint preparation: S1: Preparing the first coating: Accurately weigh an appropriate amount of the first coating base, place it in a clean, dry container that is easy to stir, add a curing agent and a diluent to the first coating base, and stir to obtain the first coating; S2: Prepare the second coating: Accurately weigh an appropriate amount of the second coating base, place it in a clean container that is easy to stir, add a curing agent and a diluent to the second coating base, and stir to obtain the second coating; S3: Viscosity test: Test the viscosity of the first coating and the second coating respectively. If the viscosity does not meet the working requirements, adjust the coating to a suitable working viscosity by adding an appropriate amount of diluent; (3) Paint spraying: spray the first paint evenly on the pre-treated substrate surface. After spraying, dry the workpiece and then bake the dried workpiece in a baking environment at 30-35°C for 1.5-2 hours to obtain the first coating. After cooling, spray the second paint evenly on the first coating under the same spraying conditions. After spraying, dry and bake the workpiece in the same way to obtain the anti-aging sealing gasket.

3. The method for manufacturing an anti-aging sealing gasket according to claim 2, characterized in that: The mass ratio of the first coating main agent to the curing agent is 100:10-15; the mass ratio of the second coating main agent to the curing agent is 100:20-25.

4. The method for manufacturing an anti-aging sealing gasket according to claim 2, characterized in that: The stirring time in step S1 is 5-15 minutes, and the stirring speed is 500-1000 rpm.

5. The method for manufacturing an anti-aging sealing gasket according to claim 2, characterized in that: The first coating main agent is S06-N-1 polyurethane thick film primer, and the second coating main agent is S04-60 acrylic polyurethane semi-gloss magnetic paint.

6. The method for manufacturing an anti-aging sealing gasket according to claim 2, characterized in that: The spraying is to transfer the first coating or the second coating with adjusted viscosity to a spraying device for spraying. The spraying pressure is 0.2-0.5 MPa, the spraying distance is 20-40 cm, and the spraying angle is 45-90 degrees.

7. The method for manufacturing an anti-aging sealing gasket according to claim 2, characterized in that: The curing agent is G-1 curing agent, and the diluent is X-11 polyurethane paint diluent.

8. The method for manufacturing an anti-aging sealing gasket according to claim 2, characterized in that: In the step S2, after adding the curing agent and the diluent, the prepared coating is polished with 100# sandpaper and then stirred.

9. The method for manufacturing an anti-aging sealing gasket according to claim 2, characterized in that: The working viscosity in step S3 is 0.00135-0.00225 Pa·s.

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