A shield segment sealing gasket with high resilience and compression deformation resistance and a preparation method thereof

Abstract

The application relates to the technical field of waterproof materials for shield tunnel engineering, and discloses a shield segment sealing gasket with high resilience and compression deformation resistance and a preparation method, which is made of solid ethylene-propylene-diene copolymer, reactive pre-dispersed masterbatch, carbon black and peroxide vulcanizing agent and the like. The masterbatch comprises carbon black, zinc methacrylate, liquid ethylene-propylene-diene rubber and alpha-methylstyrene dimer. In the application, an ionic and covalent double crosslinking network is constructed through in-situ polymerization, and reactive plasticization is realized by using liquid rubber, so that the volume shrinkage problem caused by the migration of traditional plasticizers is solved. In combination with a specific pre-dispersing process, the material has excellent compression permanent deformation resistance and long-term dimensional stability, and the safety and durability of tunnel sealing are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of waterproof materials technology for shield tunnel engineering, and in particular to a high-resilience shield segment sealing gasket resistant to compression deformation and its preparation method. Background Technology

[0002] Shield tunneling has become dominant in urban subway and large underwater tunnel construction due to its high safety and minimal environmental impact. The waterproofing performance of the segment joints directly determines the tunnel's operational safety and structural lifespan, and its core relies on the elastic rubber gaskets embedded in the segment grooves. Considering that underground infrastructure typically requires a design service life of up to 100 years, this places extremely stringent requirements on the long-term stability of the gasket materials, especially their resistance to stress relaxation and volume retention under long-term high compressive stress.

[0003] Currently, EPDM rubber, due to its saturated main chain structure, possesses excellent resistance to aging, hydrolysis, and chemical media, making it the preferred base material for tunnel segment gaskets. However, in existing industrial production systems, to reduce the Mooney viscosity of rubber to improve processing fluidity and adjust the finished product to meet design specifications, petroleum-based softening plasticizers such as paraffin oil or naphthenic oil are commonly used in formulations. These small-molecule plasticizers exist only as physical fillers between rubber molecular chains and do not form chemical bonds with the polymer network. During the long service life of the tunnel, under the seepage of ground water pressure and the continuous high compressive stress at the segment joints, these free small-molecule plasticizers tend to gradually migrate to the material surface, seep out, or be extracted by the environmental medium. This "oil seepage" phenomenon not only leads to irreversible volume shrinkage and hardening of the gasket but also directly causes a significant decrease in pressure at the sealing contact surface, ultimately causing water leakage accidents at tunnel joints.

[0004] To address the aforementioned issues of plasticizer migration and stress relaxation, the industry has attempted to introduce reactive metal salts (such as zinc methacrylate) or crosslinkable liquid rubbers to replace inert plasticizers. While zinc methacrylate can theoretically improve resilience by constructing an ionic crosslinking network through in-situ polymerization, as an extremely light, micron-sized powder with very high surface energy, it is prone to electrostatic adsorption and agglomeration during industrial mixing, resulting in significant dust dispersion and difficulty in achieving homogeneous dispersion in a viscous rubber matrix, often leading to large variations in the mechanical properties of the finished product. On the other hand, if liquid rubber is directly added as a modifier, the significant viscosity difference between it and the solid base rubber easily forms a lubricating film within the mixer cavity, causing rotor slippage, resulting in shear field failure and preventing filler dispersion. Therefore, existing technologies struggle to simultaneously achieve long-term anti-migration properties of the plasticizer and high resilience and low deformation characteristics of the material while ensuring stability during industrial processing. Summary of the Invention

[0005] The technical problem solved by this invention is that existing shield tunnel segment sealing gaskets are prone to stress relaxation under long-term high-pressure environments, and traditional liquid plasticizers tend to migrate to the surface over time, resulting in material volume shrinkage and decreased sealing performance.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a high-resilience, compression-resistant shield tunnel segment sealing gasket, made from raw materials comprising the following parts by weight: 100 parts of solid ethylene-propylene-diolefin copolymer; 65 to 71 parts of reactive pre-dispersed masterbatch; 32.5 to 35 parts of carbon black; 4 to 6 parts of zinc oxide; 0.5 to 1.5 parts of stearic acid; 2 to 3 parts of antioxidant; and 4.5 to 6.5 parts of peroxide curing agent;

[0008] The reactive predispersed masterbatch is made from the following components in parts by weight: 22.5 to 25 parts carbon black, 18 to 30 parts zinc methacrylate, 15 to 22 parts liquid ethylene propylene diene monomer (EPDM) rubber, and 1.0 to 1.2 parts α-methylstyrene dimer.

[0009] The core concept of this technical solution lies in using reactive pre-dispersed masterbatch technology to solve the problem of dispersing highly active monomers, while constructing a double cross-linked network in the rubber matrix and achieving chemical fixation of liquid phase components.

[0010] Specifically, zinc methacrylate, as a co-crosslinking agent possessing both metal ionic properties and unsaturated double bonds, undergoes in-situ polymerization initiated by peroxides and is grafted onto the molecular chains of solid ethylene-propylene-diene copolymers. This reaction not only generates carbon-carbon covalent bonds that maintain the strength of the material's skeleton, but its polar metal ionic groups also aggregate in the matrix to form ionic clusters. These ionic bonds, acting as reversible crosslinking points, dissipate energy through dissociation when the material is subjected to deformation, while the covalent bonds maintain resilience. The synergistic effect of these two factors significantly improves the material's modulus and resistance to compressive stress.

[0011] To address the issue of plasticizer migration, this solution does not employ traditional physical plasticizers (such as paraffin oil), but instead introduces liquid EPDM rubber. In the initial stages of mixing and processing, the liquid EPDM rubber, with its low viscosity, exerts physical wetting and plasticizing effects, promoting filler dispersion. During the vulcanization stage, the unsaturated double bonds on its molecular chains participate in the cross-linking reaction, permanently fixing it within the three-dimensional network structure through chemical bonding. This reactive plasticizing mechanism eliminates the risk of small molecule precipitation at its source, ensuring the gasket maintains stability in volume and hardness during long-term service.

[0012] To control the extremely high reactivity of zinc methacrylate, α-methylstyrene dimer was introduced into the formulation. This component utilizes an addition-fragmentation chain transfer mechanism to capture active free radicals in the early stages of the reaction, thereby delaying scorch and regulating the length of grafted chains, preventing uneven material properties caused by localized explosive polymerization.

[0013] The microscopic chemical reaction pathways that occur in the material during vulcanization are as follows:

[0014] Step 1: Peroxide sulfide decomposes at high temperature to generate primary free radicals (RO·);

[0015] Step 2: Primary free radicals abstract hydrogen atoms from the molecular chains of solid and liquid ethylene-propylene-diolefin copolymers to generate macromolecular active centers (EPDM·).

[0016] Step 3: Zinc methacrylate (ZDMA) undergoes homopolymerization or grafting reaction under free radical initiation (EPDM· + nZDMA → EPDM-g-(ZDMA)n·).

[0017] Step 4: α-Methylstyrene dimer (MSD) intervenes in the chain growth process, limiting the size of the ZDMA polymer phase region through chain scission transfer (R·+MSD→P+D·).

[0018] Step 5: The components are eventually cross-linked to form an interpenetrating network structure with solid rubber as the backbone, grafted with zinc polymethacrylate and chemically bonded to liquid rubber.

[0019] Preferably, the third monomer of the solid ethylene-propylene-diolefin copolymer is 5-ethylidene-2-norbornene, the ethylene content is 65wt% to 75wt%, the 5-ethylidene-2-norbornene content is 4.5wt% to 5.5wt%, and the Mooney viscosity ML(1+4) at 125°C is 70 to 90; the number average molecular weight of the liquid ethylene propylene diene monomer (EPDM) rubber is 4000 to 7000 Da, the Brookfield viscosity at 50°C is 100 to 500 Pa·s, and the iodine value is 10 to 20 g / 100 g; the particle size D50 of the zinc methacrylate is less than 10 μm.

[0020] The use of a matrix rubber with high ethylene content and high Mooney viscosity aims to impart excellent raw rubber strength and filler tolerance to the material, while the high content of the third monomer ensures a high vulcanization rate, enabling the material to set quickly. The accompanying liquid EPDM rubber, with its specific molecular weight range, possesses suitable fluidity at room temperature, allowing it to fully wet micron-sized zinc methacrylate powder and fill carbon black pores. This prevents powder dispersion and promotes the nanoscale dispersion of active monomers in the matrix, laying the physical foundation for subsequent uniform reactions.

[0021] Preferably, the peroxide sulfiding agent is bis(tert-butylperoxyisopropyl)benzene; the carbon black is fast-pressing furnace black N550; and the chemical name of the α-methylstyrene dimer is 2,4-diphenyl-4-methyl-1-pentene.

[0022] Bis(tert-butylperoxide isopropyl)benzene was chosen because of its high crosslinking efficiency and the absence of irritating odors in its decomposition products, meeting environmental protection and construction requirements. Fast extrusion black N550 possesses moderate structure and specific surface area. As a masterbatch carrier, it effectively adsorbs liquid phase components; as a reinforcing agent, it imparts good surface finish and dimensional stability to extruded products, avoiding processing difficulties caused by high-reinforcing carbon black or insufficient mechanical properties caused by low-reinforcing carbon black.

[0023] Preferably, the antioxidant is a mixture of antioxidant RD and antioxidant MB.

[0024] The combined use of antioxidants RD and MB can produce a synergistic effect. The former mainly captures free radicals generated by thermo-oxidative aging, while the latter focuses on decomposing hydrogen peroxide. This combination effectively blocks the chain reaction of rubber aging, thereby significantly extending the service life of the gasket in underground humid and oxidizing environments.

[0025] Secondly, the present invention provides a method for preparing a shield tunnel segment sealing gasket with high resilience and resistance to compression deformation, comprising the following steps:

[0026] Step 1, Preparation of reactive predispersible masterbatch: Carbon black and zinc methacrylate are dry-mixed in a mixer to obtain a mixed powder; liquid EPDM rubber and α-methylstyrene dimer are pre-mixed to prepare a mixed liquid; the mixed liquid is sprayed into the mixed powder and stirred until the material is transformed into particles without free liquid to obtain reactive predispersible masterbatch;

[0027] Step 2, First stage of mixing: Solid ethylene-propylene-diolefin copolymer, zinc oxide, stearic acid, antioxidant and carbon black are put into a mixer for mixing. Then, the reactive pre-dispersed masterbatch obtained in Step 1 is added and mixing is continued. When the discharge temperature reaches 145℃ to 150℃, the masterbatch is discharged to obtain the first stage of compound.

[0028] Step 3, Second-stage vulcanization: The first-stage compound is rolled on a two-roll mill, peroxide vulcanizing agent is added, and after being mixed evenly, it is sheeted out and left to stand.

[0029] Step 4, vulcanization molding: The rubber compound after being left to stand is vulcanized under high temperature and high pressure.

[0030] This preparation process focuses on solving the processing challenges of dispersing highly active powders and liquid additives in a rubber matrix, which is difficult and prone to scorching. In conventional mixing, directly adding liquid EPDM rubber often causes the internal mixer rotor to slip, which not only reduces shearing efficiency but also results in uneven material mixing. At the same time, lightweight zinc methacrylate powder is prone to agglomeration and is difficult to achieve an ideal dispersion state in the matrix.

[0031] To overcome the aforementioned shortcomings, this invention employs a pre-dispersion strategy of "liquid-phase adsorption-solid-phase support." This strategy utilizes the capillary action generated by the well-developed porous structure of carbon black to forcibly adsorb liquid EPDM rubber pre-dissolved in α-methylstyrene dimer into the interior of the carbon black pores, thereby transforming the originally difficult-to-handle liquid component into macroscopically dry, highly fluid solid particles. This physical transformation process not only eliminates the slippage caused by the liquid but, more importantly, achieves spatially positioned encapsulation of the reactive monomer (zinc methacrylate) by the reaction control agent (α-methylstyrene dimer). Since the α-methylstyrene dimer dissolves in the liquid rubber layer coated on the surface of zinc methacrylate, this ensures that the polymerization inhibitor remains close to the active reaction center during subsequent high-temperature mixing and vulcanization induction periods. This allows for precise control of the initiation time of the free radical reaction, effectively widening the processing safety window.

[0032] In the mixing process, this invention balances the oil absorption saturation of the masterbatch and the reinforcing requirements of the final rubber compound by introducing carbon black in stages (partially introduced into the masterbatch and supplemented in the first stage of mixing). In particular, the control of the discharge temperature (145℃ to 150℃) ensures that zinc methacrylate can soften at this temperature and undergo phase recombination under strong shear force to achieve nanoscale dispersion, while avoiding uncontrollable thermal crosslinking reactions triggered by excessively high temperatures, thus preserving sufficient crosslinking activity for the subsequent second-stage vulcanization.

[0033] Preferably, in step 1: the dry mixing speed is 500 to 600 revolutions per minute, and the time is 1 to 2 minutes; the speed when spraying the mixture is increased to 1000 to 1200 revolutions per minute, and the stirring time is maintained for 3 to 5 minutes; the material temperature is controlled to be below 70°C during the stirring process.

[0034] The high-speed shearing process here utilizes a powerful centrifugal force to force the liquid to atomize and rapidly penetrate the powder layer, preventing localized agglomeration. Controlling the material temperature below 70°C maintains the system's chemical inertness, ensuring that zinc methacrylate does not prepolymerize during the physical mixing stage and that the liquid rubber does not oxidize or deteriorate, thus guaranteeing the quality stability of the masterbatch as a "reaction precursor."

[0035] Preferably, in step 2: the initial temperature of the internal mixer is set to 50°C and the rotation speed is set to 60 revolutions per minute; first, solid ethylene-propylene-diolefin copolymer is added and mixed for 60 seconds, then zinc oxide, stearic acid, antioxidant and carbon black are added and mixed for another 90 seconds, and finally reactive pre-dispersed masterbatch is added and mixed for 180 seconds.

[0036] The specific order of material addition aims to create an optimal rheological environment. High-viscosity solid rubber and reinforcing carbon black are added first, utilizing high shear forces to rapidly raise the temperature and establish the modulus and viscosity of the base compound. Subsequently, reactive pre-dispersed masterbatch is added. At this point, the base compound already possesses suitable fluidity, facilitating the rapid incorporation and melting dispersion of the masterbatch particles into the matrix. This post-addition of masterbatch also minimizes the residence time of active components under high temperature and high shear conditions, further reducing the risk of early scorching.

[0037] Preferably, in step 3: the roller temperature of the open mill is controlled at 50°C to 60°C; the uniform mixing operation includes three cuts on each side and five triangular wraps; the resting time after sheeting is 24 hours. Preferably, in step 4: the vulcanization temperature is 170°C, the pressure is 15 MPa, and the time is 10 to 12 minutes.

[0038] Low-temperature open milling combined with multiple turning operations (thin pass, triangular wrapping) is to ensure that the peroxide vulcanizing agent is evenly distributed at low temperatures and does not decompose prematurely. The 24-hour rest period is to allow the rubber molecular chains to fully relax after undergoing severe shearing, and to promote the concentration balance of the compounding agents through diffusion, eliminating internal stress. This is crucial for ensuring the dimensional accuracy and long-term compression set performance of the final sealing gasket under high pressure.

[0039] In summary, the present invention has at least one of the following beneficial technical effects:

[0040] 1. This invention constructs a dual network structure in a rubber matrix by in-situ polymerization of zinc methacrylate, in which carbon-carbon covalent bonds and ionic bonds coexist. The energy dissipation mechanism of ionic bonds and the elastic recovery ability of covalent bonds work synergistically to significantly reduce the compression set of the material and greatly extend the service life of the gasket under long-term high stress conditions.

[0041] 2. This invention utilizes liquid EPDM rubber to replace traditional inert physical plasticizers, permanently fixing them in the polymer network through chemical bonding; this reactive plasticizing eliminates the risk of small molecule plasticizers migrating to the surface over time, ensuring that the gasket maintains volume stability over decades of service and avoiding seal failure due to material shrinkage.

[0042] 3. This invention develops a reactive pre-dispersed masterbatch preparation process based on liquid-phase adsorption-solid-phase support, which effectively solves the problems of slippage of liquid rubber during internal mixing and easy agglomeration of highly active powders; combined with the slow-release regulation of α-methylstyrene dimer, it achieves nanoscale uniform dispersion of active components, while broadening the processing scorch safety window and ensuring the uniformity of product quality. Attached Figure Description

[0043] Figure 1 This is a comparison of the infrared spectra of the extracts from Example 1 and Comparative Example 1 of the present invention;

[0044] Figure 2 The diagram shows a comparison of the processing rheological behavior and mechanical property stability between Example 1 and Comparative Example 3 of the present invention; wherein, (a) is a comparison of the torque-time curves during the Mooney viscosity test; and (b) is a comparison of the tensile strength scatter distribution of 10 randomly sampled points.

[0045] Figure 3 This is a comparison chart of the compression set rates of Examples 1-4 and Comparative Examples 1-4 under different thermal aging conditions.

[0046] Figure 4 These are the compressive stress relaxation curves of Embodiment 1 and Comparative Examples 1 and 2 of the present invention under a 100°C environment. Detailed Implementation

[0047] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0048] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0049] Ethylene-propylene-diolefin copolymer (EPDM), CAS No. 25038-36-2, is used in two different specifications in this embodiment of the invention:

[0050] Specification A is a solid raw rubber, with the third monomer being 5-ethylidene-2-norbornene, ethylene content of 65wt%~75wt%, ENB content of 4.5wt%~5.5wt%, and Mooney viscosity ML(1+4) at 125℃ of 70~90;

[0051] Specification B is a liquid rubber with a number average molecular weight of 4000-7000 Da, a Brookfield viscosity of 100-500 Pa·s at 50℃, and an iodine value of 10-20 g / 100g.

[0052] Zinc methacrylate (ZDMA), CAS No. 13189-00-9, purity greater than 98%, particle size D50 less than 10μm.

[0053] α-Methylstyrene dimer (MSD), CAS No. 6362-80-7, chemical name 2,4-diphenyl-4-methyl-1-pentene, purity greater than 96%.

[0054] Quick-pressed oven black (N550), CAS No. 1333-86-4, iodine absorption value 40~46g / kg.

[0055] Bis(tert-butylperoxyisopropyl)benzene (BIPB), CAS No. 25155-25-3, purity greater than 96%.

[0056] Zinc oxide (CAS No. 1314-13-2), stearic acid (CAS No. 57-11-4), antioxidant RD (CAS No. 26780-96-1) and antioxidant MB (CAS No. 583-39-1) are all commercially available industrial-grade products.

[0057] Preparation Example 1:

[0058] This preparation example provides a method for preparing a reactive predispersed masterbatch, including the following steps:

[0059] (1) Weigh 22.5 parts by weight of fast-pressed furnace black (N550) and 25 parts by weight of zinc methacrylate (ZDMA) and put them into a high-speed mixer with a heating / cooling jacket. Set the speed to 500 rpm and dry mix for 1.5 minutes to obtain a mixed powder.

[0060] (2) Weigh 20 parts by weight of liquid EPDM rubber (specification B) and 1.0 part by weight of α-methylstyrene dimer (MSD), and mix them evenly to prepare a mixture;

[0061] (3) Increase the speed of the high-speed mixer to 1100 rpm, and slowly spray the mixture obtained in step (2) into the mixed powder in step (1) through the nozzle, keep the high-speed stirring for 4 minutes, and control the material temperature to be below 70℃.

[0062] (4) When the material changes from a wet state to a loose granular state without free liquid, stop stirring and discharge the material to obtain reactive predispersed masterbatch.

[0063] Preparation Example 2:

[0064] This preparation example provides a method for preparing a reactive predispersed masterbatch, including the following steps:

[0065] (1) Weigh 24 parts by weight of fast-pressed furnace black (N550) and 18 parts by weight of zinc methacrylate (ZDMA) and put them into a high-speed mixer with a heating / cooling jacket. Set the speed to 550 rpm and dry mix for 1 minute to obtain a mixed powder.

[0066] (2) Weigh 22 parts by weight of liquid EPDM rubber (specification B) and 1.0 parts by weight of α-methylstyrene dimer (MSD), and mix them evenly to prepare a mixture;

[0067] (3) Increase the speed of the high-speed mixer to 1200 rpm, and slowly spray the mixture obtained in step (2) into the mixed powder in step (1) through the nozzle, keep the high-speed stirring for 5 minutes, and control the material temperature to be below 70℃.

[0068] (4) When the material changes from a wet state to a loose granular state without free liquid, stop stirring and discharge the material to obtain reactive predispersed masterbatch.

[0069] Preparation Example 3:

[0070] This preparation example provides a method for preparing a reactive predispersed masterbatch, including the following steps:

[0071] (1) Weigh 25 parts by weight of quick-pressed furnace black (N550) and 30 parts by weight of zinc methacrylate (ZDMA) and put them into a high-speed mixer with a heating / cooling jacket. Set the speed to 600 rpm and dry mix for 2 minutes to obtain a mixed powder.

[0072] (2) Weigh 15 parts by weight of liquid EPDM rubber (specification B) and 1.0 parts by weight of α-methylstyrene dimer (MSD), and mix them evenly to prepare a mixture;

[0073] (3) Increase the speed of the high-speed mixer to 1000 rpm, and slowly spray the mixture obtained in step (2) into the mixed powder in step (1) through the nozzle, keep the high-speed stirring for 3 minutes, and control the material temperature to be below 70℃.

[0074] (4) When the material changes from a wet state to a loose granular state without free liquid, stop stirring and discharge the material to obtain reactive predispersed masterbatch.

[0075] Preparation Example 4:

[0076] This preparation example provides a method for preparing a reactive predispersed masterbatch, including the following steps:

[0077] (1) Weigh 22.5 parts by weight of fast-pressed furnace black (N550) and 25 parts by weight of zinc methacrylate (ZDMA) and put them into a high-speed mixer with a heating / cooling jacket. Set the speed to 500 rpm and dry mix for 1.5 minutes to obtain a mixed powder.

[0078] (2) Weigh 20 parts by weight of liquid EPDM rubber (specification B) and 1.2 parts by weight of α-methylstyrene dimer (MSD), and mix them evenly to prepare a mixture;

[0079] (3) Increase the speed of the high-speed mixer to 1100 rpm, and slowly spray the mixture obtained in step (2) into the mixed powder in step (1) through the nozzle, keep the high-speed stirring for 4 minutes, and control the material temperature to be below 70℃.

[0080] (4) When the material changes from a wet state to a loose granular state without free liquid, stop stirring and discharge the material to obtain reactive predispersed masterbatch.

[0081] Example 1:

[0082] This embodiment provides a method for preparing a shield tunnel segment sealing gasket with high resilience and resistance to compression deformation, including the following steps:

[0083] (1) First stage of mixing: Set the internal mixer temperature to 50°C and the speed to 60 rpm. Add 100 parts by weight of ethylene-propylene-diolefin copolymer (EPDM, specification A) and mix under pressure for 60 seconds; then add 5 parts by weight of zinc oxide, 1 part by weight of stearic acid, 1.5 parts by weight of antioxidant RD, 1.0 part by weight of antioxidant MB and 35 parts by weight of fast-pressing furnace black (N550), and continue mixing for 90 seconds;

[0084] (2) Using masterbatch together: Add 68.5 parts by weight of the reactive predispersed masterbatch obtained in Preparation Example 1 (containing about 25 parts of ZDMA) to the internal mixer and continue mixing for 180 seconds to ensure that the masterbatch is evenly dispersed and there is no slippage. When the discharge temperature reaches 145℃~150℃, discharge the masterbatch to obtain a first-stage compound.

[0085] (3) Second stage vulcanization: Wrap the first stage compound rubber on the open mill with rollers, control the roller temperature at 50℃~60℃, add 5.5 parts by weight of bis(tert-butylperoxyisopropyl)benzene (BIPB), cut the left and right blades three times each, make the triangular wrap five times, thinly pass through the sheet, and let it stand for 24 hours.

[0086] (4) Vulcanization molding: Place the rubber material after it has been left to stand in a flat vulcanizing machine and vulcanize it for 10 minutes at 170°C and 15MPa pressure (T90×1.2) to obtain a shield tunnel segment sealing gasket with high resilience and resistance to compression deformation.

[0087] Example 2:

[0088] This embodiment provides a method for preparing a shield tunnel segment sealing gasket with high resilience and resistance to compression deformation, including the following steps:

[0089] (1) First stage of mixing: Set the internal mixer temperature to 50°C and the speed to 60 rpm. Add 100 parts by weight of ethylene-propylene-diolefin copolymer (EPDM, specification A) and mix under pressure for 60 seconds; then add 5 parts by weight of zinc oxide, 1 part by weight of stearic acid, 1.5 parts by weight of antioxidant RD, 1.0 part by weight of antioxidant MB and 33.5 parts by weight of fast-pressing furnace black (N550), and continue mixing for 90 seconds;

[0090] (2) Combined use of masterbatch: Add 65 parts by weight of the reactive predispersed masterbatch (containing about 18 parts of ZDMA) obtained in Preparation Example 2 to the internal mixer, continue mixing for 180 seconds, and discharge the masterbatch when the discharge temperature reaches 145℃~150℃ to obtain a first-stage compound.

[0091] (3) Second stage vulcanization: Wrap the first stage compound rubber on the open mill with rollers, control the roller temperature at 50℃~60℃, add 4.5 parts by weight of bis(tert-butylperoxyisopropyl)benzene (BIPB), cut the left and right blades three times each, make the triangular wrap five times, and then sheet it out in thin strips and let it stand for 24 hours.

[0092] (4) Vulcanization molding: Place the rubber material after it has been left to stand in a flat vulcanizing machine and vulcanize it for 10 minutes at 170°C and 15MPa pressure to obtain a shield tunnel segment sealing gasket with high resilience and resistance to compression deformation.

[0093] Example 3:

[0094] This embodiment provides a method for preparing a shield tunnel segment sealing gasket with high resilience and resistance to compression deformation, including the following steps:

[0095] (1) First stage of mixing: Set the internal mixer temperature to 50°C and the speed to 60 rpm. Add 100 parts by weight of ethylene-propylene-diolefin copolymer (EPDM, specification A) and mix under pressure for 60 seconds; then add 5 parts by weight of zinc oxide, 1 part by weight of stearic acid, 1.5 parts by weight of antioxidant RD, 1.0 part by weight of antioxidant MB and 32.5 parts by weight of fast-pressing furnace black (N550), and continue mixing for 90 seconds;

[0096] (2) Combined use of masterbatch: Add 71 parts by weight of the reactive predispersed masterbatch obtained in Preparation Example 3 (containing about 30 parts of ZDMA) to the internal mixer, continue mixing for 180 seconds, and discharge the masterbatch when the discharge temperature reaches 145℃~150℃ to obtain a first-stage compound;

[0097] (3) Second stage vulcanization: Wrap the first stage compound rubber on the open mill with rollers, control the roller temperature at 50℃~60℃, add 6.5 parts by weight of bis(tert-butylperoxyisopropyl)benzene (BIPB), cut the left and right blades three times each, make the triangular wrap five times, and then sheet it out in thin strips and let it stand for 24 hours.

[0098] (4) Vulcanization molding: The rubber material after being left to stand is placed in a flat vulcanizing machine and vulcanized for 12 minutes at 170°C and 15MPa pressure to obtain a shield tunnel segment sealing gasket with high resilience and resistance to compression deformation.

[0099] Example 4:

[0100] This embodiment provides a method for preparing a shield tunnel segment sealing gasket with high resilience and resistance to compression deformation, including the following steps:

[0101] (1) First stage of mixing: Set the internal mixer temperature to 50°C and the speed to 60 rpm. Add 100 parts by weight of ethylene-propylene-diolefin copolymer (EPDM, specification A) and mix under pressure for 60 seconds; then add 5 parts by weight of zinc oxide, 1 part by weight of stearic acid, 1.5 parts by weight of antioxidant RD, 1.0 part by weight of antioxidant MB and 35 parts by weight of fast-pressing furnace black (N550), and continue mixing for 90 seconds;

[0102] (2) Using masterbatch together: Add 68.7 parts by weight of the reactive predispersed masterbatch obtained in Preparation Example 4 to the internal mixer, continue mixing for 180 seconds, and discharge the masterbatch when the discharge temperature reaches 145℃~150℃ to obtain a first-stage compound.

[0103] (3) Second stage vulcanization: Wrap the first stage compound rubber on the open mill with rollers, control the roller temperature at 50℃~60℃, add 5.5 parts by weight of bis(tert-butylperoxyisopropyl)benzene (BIPB), cut the left and right blades three times each, make the triangular wrap five times, thinly pass through the sheet, and let it stand for 24 hours.

[0104] (4) Vulcanization molding: Place the rubber material after it has been left to stand in a flat vulcanizing machine and vulcanize it for 10 minutes at 170°C and 15MPa pressure to obtain a shield tunnel segment sealing gasket with high resilience and resistance to compression deformation.

[0105] Comparative Example 1:

[0106] This comparative example provides a method for preparing a shield tunnel segment sealing gasket. Compared with Example 1, the difference is that when preparing the reactive predispersed masterbatch, an equal weight of paraffin oil (brand name Sunpar 2280) is used to replace liquid EPDM rubber (specification B). The other raw material types, amounts, and preparation processes are the same.

[0107] Comparative Example 2:

[0108] This comparative example provides a method for preparing a shield tunnel segment sealing gasket. The difference from Example 1 is that α-methylstyrene dimer (MSD) was not added when preparing the reactive predispersed masterbatch, while the other raw material types, amounts, and preparation processes are the same.

[0109] Comparative Example 3:

[0110] This comparative example provides a method for preparing a shield tunnel segment sealing gasket. Compared with Example 1, the difference is that the preparation step of reactive pre-dispersed masterbatch is omitted, and a direct mixing method is adopted. Specifically, in the first mixing step (1), fast-pressing furnace black (N550), zinc methacrylate (ZDMA), liquid EPDM rubber (specification B) and α-methylstyrene dimer (MSD) in the same amount as the masterbatch formulation described in Example 1 are directly put into the internal mixer and mixed with solid EPDM. The types and total amounts of other raw materials are the same.

[0111] Comparative Example 4:

[0112] This comparative example provides a method for preparing a shield tunnel segment sealing gasket. Compared with Example 1, the difference is that zinc methacrylate (ZDMA) was not added when preparing the reactive predispersed masterbatch. In order to compensate for the hardness loss after removing ZDMA, 20 parts by weight of fast-pressing black (N550) were added. The other raw materials and preparation process are the same.

[0113] Test Example 1:

[0114] The experimental steps are as follows:

[0115] (1) Take the vulcanized samples of Example 1, Comparative Example 1 and Comparative Example 4, cut them into particles of about 1 mm × 1 mm × 1 mm, weigh the initial mass m0 of about 2.0 g, accurate to 0.0001 g, wrap it with filter paper of known mass and put it into Soxhlet extractor.

[0116] (2) Add 150 mL of toluene solvent to the extractor flask, set the heating temperature to 115 °C, and keep it under reflux for 72 hours to ensure that the small molecule components and free plasticizers that have not participated in cross-linking in the rubber matrix are fully dissolved.

[0117] (3) After extraction, remove the filter paper package and dry it in a vacuum oven at 80°C until constant weight. Weigh the mass of the residue m1 and calculate the sol fraction according to the formula (m0-m1) / m0×100%. This value reflects the proportion of components in the system that are not anchored by chemical bonds.

[0118] (4) The extract was concentrated by rotary evaporation, coated onto a potassium bromide (KBr) window, and analyzed by Fourier transform infrared spectroscopy (FTIR) at 4000–400 cm⁻¹. -1Scanning was performed within a certain range to analyze the chemical composition characteristics of the extract, with a focus on the 2800–3000 cm⁻¹ area. -1 (CH stretching vibration) and 1700cm -1 The intensity of the absorption peak near the carbonyl or ester group.

[0119] The experimental results are shown in Table 1.

[0120] Table 1. Sol fraction and extract composition analysis data of the examples and comparative examples:

[0121]

[0122] Combining the quantitative data in Table 1 with Figure 1 The spectral qualitative analysis clearly reveals the effectiveness of the reactive plasticizing mechanism of this invention. The high sol fraction of 14.10% in Comparative Example 1 indicates the presence of a large number of components not bound by a network. Figure 1 The spectral characteristics of the solid black line in the middle further confirm this, at 2920 cm⁻¹. -1 and 2850cm -1 An extremely strong CH stretching vibration absorption peak appeared at 1460 cm⁻¹, and at 1460 cm⁻¹... -1 The presence of distinct bending vibration peaks indicates that these characteristics closely match the standard spectrum of paraffin oil. This suggests that in traditional physical plasticizing systems, paraffin oil only fills the gaps between rubber molecular chains and is highly prone to migration and precipitation under solvent or long-term pressure conditions. This is the root cause of the later volume shrinkage and hardening of the gasket.

[0123] In contrast, although Example 1 introduced a large amount of liquid EPDM as a processing aid into the formulation, its sol fraction was only 3.79%. More importantly, Figure 1 The gray dashed line indicates that the extract exhibits extremely weak infrared absorption, almost touching the baseline, with no obvious characteristic peaks of organic matter. This significant difference demonstrates that the double bonds on the liquid EPDM molecular chains underwent a chemical grafting reaction with the solid EPDM matrix under the initiation of peroxides. The liquid component transforms from a free state to a bound state, anchoring itself within a three-dimensional cross-linked network. This chemical bonding not only eliminates the risk of small molecule migration but also further enhances the network's density through the ionic clusters formed by ZDMA, thereby endowing the material with excellent long-term dimensional stability and resistance to compressive deformation.

[0124] Test Example 2:

[0125] The experimental steps are as follows:

[0126] (1) From the compound (unvulcanized) prepared in Example 1 and Comparative Example 3, rubber compounds from different parts were randomly selected as test samples. First, a Mooney viscometer was used to test the rubber at 100°C. After preheating for 1 minute and rotating for 4 minutes, the Mooney viscosity value (ML) was recorded. 1+4 ) and Mooney scorch time (t) 10 This is used to evaluate the flowability of the rubber compound during processing and its early scorch resistance.

[0127] (2) In order to quantify the uniformity of the dispersion of fillers and reactive components in the matrix, a batch stability test was conducted using a multi-point sampling method. Ten samples, each weighing approximately 50g, were taken at intervals from the same batch of compounding in Example 1 and Comparative Example 3.

[0128] (3) Add vulcanizing agent to each of the 10 samples according to their respective two-stage processes, and prepare standard vulcanized sheets on a flat vulcanizing machine. Then cut them into dumbbell-shaped specimens and test their tensile strength using an electronic universal testing machine.

[0129] (4) Record 10 tensile strength data for each group, calculate the arithmetic mean (Mean), standard deviation (SD) and coefficient of variation (CV value, i.e. standard deviation divided by mean). The lower the CV value, the more uniform the micro-dispersion of ZDMA and liquid rubber in the matrix and the more stable the macroscopic properties.

[0130] The experimental results are shown in Table 2.

[0131] Table 2. Processing rheology and batch stability test data of Example 1 and Comparative Example 3:

[0132]

[0133] Based on the statistical data in Table 2 and Figure 2 The curve characteristics of Example 1 and Comparative Example 3 show drastically different properties in terms of processing performance and microdispersibility, confirming the necessity of pre-dispersion process in processing highly filled liquid / ZDMA systems.

[0134] Comparative Example 3 uses a direct mixing method, such as... Figure 2 As shown in (a), its Mooney viscosity curve exhibits irregular low-value oscillations, with a final viscosity of only 32.1. This does not indicate good flowability of the compound, but rather a typical "wall slip" phenomenon: a large amount of liquid EPDM and ZDMA powder form a lubricating layer in the initial mixing stage within the internal mixer, causing the rotor to be unable to apply effective shear force to the compound, resulting in the material slipping and spinning idly in the mixing chamber. This ineffective mixing directly leads to extremely uneven dispersion of components, such as... Figure 2As shown in (b), the tensile strength data of Comparative Example 3 exhibits extremely high dispersion, with a coefficient of variation (CV) as high as 16.83%. Some samples showed strengths as low as 9.50 MPa, presumably due to microscopic defects formed by liquid aggregation; while others showed higher strengths, likely due to localized ZDMA agglomeration. Furthermore, due to uneven local shear heating, the scorching time of Comparative Example 3 was shortened to 11.4 minutes, raising concerns about processing safety.

[0135] In contrast, Example 1 utilized the high oil absorption of carbon black to pre-prepare a dry powder masterbatch, locking the liquid component within the carbon black pores and fundamentally preventing processing slippage. Its Mooney curve was smooth and stable, and the viscosity value of 48.5 was within the ideal processing range, indicating that the compound underwent sufficient and uniform shearing during the mixing process. This excellent processability directly translates into superior product consistency; the tensile strength of the 10 samples from Example 1 was highly concentrated around 16.23 MPa, with a CV value of only 0.68%. This demonstrates that ZDMA, liquid EPDM, and MSD achieved nanoscale uniform dispersion in the matrix, constructing a uniform ionic / covalent dual network, thereby ensuring the reliability of the shield tunnel segment sealing gasket's performance and the predictability of its lifespan in practical engineering applications.

[0136] Test Example 3:

[0137] The experimental steps are as follows:

[0138] (1) Using a vulcanizing mold, standard compression set specimens were prepared from the rubber compounds of Examples 1-4 and Comparative Examples 1-4. The specimens were Type B specimens as specified in GB / T 7759, i.e., cylinders with a diameter of 13.0 mm and a height of 6.3 mm. The initial height h0 of each specimen was measured using a thickness gauge, accurate to 0.01 mm.

[0139] (2) Place the sample between the steel plates of the compression fixture, and control the compression rate at 25% using the limiter, i.e., the height h after compression. s It is approximately 4.72 mm.

[0140] (3) The fixtures were divided into two groups and placed in the aging chamber for testing. The first group was set to standard working conditions: 70℃ for 24 hours; the second group was set to harsh working conditions: 100℃ for 168 hours.

[0141] (4) After the test, immediately remove the clamp from the constant temperature chamber and loosen the bolts to release the compression within 30 seconds. Place the sample on a wooden board and allow it to cool and recover for 30 minutes in a standard laboratory environment (23±2℃).

[0142] (5) Measure the center height h1 of the recovered sample again. According to the formula C=(h0-h1) / (h0-h sThe compression set is calculated as () × 100%. The lower this value, the stronger the material's elastic memory and the more durable its sealing performance.

[0143] The experimental results are shown in Table 3.

[0144] Table 3. Test results of compressive permanent deformation rate of each group of samples under different working conditions:

[0145]

[0146] Based on the data in Table 3 and Figure 3 The trends of the curves reveal the significant advantages of the kinetic regulation mechanism constructed in this invention in maintaining the long-term resilience of the sealing gasket. The deformation rates of Examples 1 to 4 remained extremely low under both operating conditions. Example 1, in particular, even under extreme accelerated aging conditions of 100°C and 168 hours, only saw a slight increase in deformation rate from 12.4% to 18.9%. This high stability stems from the precise regulation of ZDMA reaction kinetics by MSD in the formulation. During vulcanization, MSD effectively inhibits premature self-aggregation of ZDMA molecules, inducing the formation of small and uniformly distributed ion clusters in the EPDM matrix. These ion clusters, acting as dynamic cross-linking points, interpenetrate and intertwine with the covalent bond network formed by the peroxide. Under pressure, they dissipate stress through the dissociation and recombination of ion bonds, and after pressure removal, the elastic memory of the covalent network drives the ion clusters to re-aggregate, thus achieving near-perfect shape recovery.

[0147] In contrast, the data for Comparative Example 2 shows a significant anomaly, with an initial deformation rate as high as 38.5% at 70°C. This is due to the lack of MSD regulation, which caused severe self-polymerization of ZDMA during the mixing and vulcanization stages, resulting in a large amount of rigid polymethyl methacrylate phase. These rigid phases not only fail to provide resilience but also disrupt the continuity of the rubber matrix, leading to irreversible plastic flow of the material under pressure.

[0148] Furthermore, the performance of Comparative Example 1 under harsh conditions further confirms the importance of chemical anchoring; although its initial deformation rate (16.2%) was acceptable, it increased dramatically to 45.8% with prolonged aging. Observation of the experimental process revealed obvious oily seepage on the surface of the Comparative Example 1 sample, confirming that physically filled paraffin oil migrates from the network gaps under high temperature and pressure, causing material volume shrinkage and loss of plasticizing protection, thus triggering severe creep. In contrast, the embodiments of this invention, through the reactive incorporation of liquid EPDM, eliminate the physical basis for small molecule migration, ensuring that the sealing gasket can maintain stable sealing reaction force during the century-long service life of underground engineering projects. This is of crucial technical significance for the waterproof safety of shield tunnels.

[0149] Test Example 4:

[0150] The experimental steps are as follows:

[0151] (1) The compound rubbers of Examples 1-4 and Comparative Examples 1-4 were vulcanized at 170°C for 10 minutes on a flat vulcanizing machine (t). 90 (+2min) to prepare a standard vulcanized film with a thickness of 2.0 mm. The film was then placed in a standard laboratory environment (23±2℃, 50±5%RH) for 24 hours to eliminate internal stress.

[0152] (2) According to GB / T 531.1-2008 standard, the film is stacked to a thickness of 6mm. Using a Shore A hardness tester, 5 points at least 6mm apart are selected on the flat surface of the sample for testing. The values ​​are read after the indenter contacts the sample for 3 seconds, and the arithmetic mean is taken as the hardness data.

[0153] (3) According to GB / T 18173.4-2010 standard, the 2mm film was cut into type II dumbbell-shaped specimens using a punching machine. Tensile tests were performed using an electronic universal testing machine equipped with a high-precision extensometer, with the tensile speed set to 500mm / min.

[0154] (4) During the test, the computer automatically records the stress-strain curve and extracts the tensile strength, elongation at break and 100% constant elongation stress. Five parallel samples are tested for each formulation. After removing outliers, the average value is taken to evaluate the balance between stiffness (modulus) and toughness (elongation) of the material.

[0155] The experimental results are shown in Table 4.

[0156] Table 4. Physical and mechanical property test data of the examples and comparative examples:

[0157]

[0158] Table 4 shows the test data demonstrating the breakthrough of this invention in solving the classic problem of the inverse relationship between strength and toughness in rubber materials. Typically, increasing the hardness and modulus of rubber often comes at the cost of sacrificing elongation, leading to brittleness. However, in Examples 1-4, the tensile strength generally exceeds 16 MPa, while the elongation at break remains above 430%, and the hardness is controlled within the ideal sealing range of 67-71 Shore A. This excellent overall performance stems from the synergistic effect of the ion clusters generated in situ by ZDMA and the grafted segments of liquid EPDM. The ionic bonds, acting as sacrificial bonds, preferentially break during stretching to dissipate a large amount of energy, thereby significantly increasing strength; while the long-chain structure of liquid EPDM endows the network with excellent flexibility and ductility, avoiding premature fracture caused by stress concentration.

[0159] In contrast, Comparative Example 2 exhibits typical hard and brittle characteristics. In the absence of MSD control, ZDMA excessively self-aggregates to form coarse, rigid particles, causing the 100% tensile stress to surge to 8.90 MPa and the hardness to reach 78.6 Shore A, but the elongation at break drops sharply to 210%. Although this material has high stiffness, it is extremely prone to brittle fracture or chipping under the high-pressure stress of shield tunnel segment assembly, and cannot meet engineering requirements.

[0160] Although Comparative Example 1 exhibits a high elongation (620%), its tensile strength and stress at a given elongation are significantly lower, classifying it as a soft and weak material. This is because paraffin oil only acts as a physical diluent, weakening intermolecular forces and failing to provide the strong reinforcing effect of ZDMA. In summary, this invention achieves a harmonious balance between high modulus and high elongation through a unique kinetic regulation and reactive plasticizing strategy, providing a material basis for shield tunnel segment sealing gaskets that combines high pressure resistance with excellent deformation adaptability.

[0161] Test Example 5:

[0162] The experimental steps are as follows:

[0163] (1) Select the standard vulcanized rubber sheets (thickness 2.0 mm) prepared in Example 1 and Comparative Example 1, and cut them into dumbbell-shaped specimens and square specimens with a side length of 50 mm that conform to GB / T528 standard. Weigh the initial mass m0 of each specimen using an electronic balance with an accuracy of 0.001%, and measure the initial hardness H0 and the initial tensile strength TS0.

[0164] (2) The sample was suspended in a hot air aging test chamber and the temperature was set to 100°C for 168 hours. Forced air circulation was maintained in the test chamber to simulate the oxidation and thermal degradation environment of the material during long-term service.

[0165] (3) After the aging cycle is over, take out the sample and let it stand for 24 hours in a standard laboratory environment (23±2℃) to allow its performance to stabilize.

[0166] (4) Observe whether there is oily seepage or blooming on the surface of the sample. Weigh the sample again m1, and measure the hardness H1 and tensile strength TS1 after aging.

[0167] (5) Calculate the mass loss rate [(m0-m1) / m0×100%], hardness change (ΔH=H1-H0), and tensile strength retention rate (TS1 / TS0×100%). These indicators are used to quantitatively evaluate the migration stability of liquid components at high temperatures and the aging resistance of materials.

[0168] The experimental results are shown in Table 5.

[0169] Table 5. Performance comparison between Example 1 and Comparative Example 1 before and after aging at 100℃ for 168h:

[0170]

[0171] According to the experimental data in Table 5, Example 1 shows significantly better stability than Comparative Example 1 in simulated long-term service environment, which verifies the core value of the chemical anchoring mechanism of this scheme in extending the service life of the gasket.

[0172] During the forced aging process at 100℃ for 168 hours, Comparative Example 1 exhibited a mass loss rate as high as 5.30%, and a noticeable greasy feel was observed on the sample surface after the experiment. This phenomenon indicates that the paraffin oil, acting as a physical plasticizer, is only weakly bonded to the EPDM matrix by van der Waals forces, and under thermal drive, it easily detaches from the molecular chain gaps and migrates to the material surface. The loss of paraffin oil directly led to a significant increase in the hardness of Comparative Example 1 by 11.4 units. Simultaneously, due to severe post-crosslinking and shrinkage of the effective load-bearing cross-section, its tensile strength abnormally increased, with a strength change rate as high as +8.5%. This volume shrinkage and modulus mutation caused by component migration are the main contributing factors to leakage of shield tunnel sealing gaskets in the later stages of service.

[0173] In contrast, Example 1 exhibited a mass loss rate of only 0.14%, which is negligible, and the hardness change was controlled within +1.7 Shore A, demonstrating extremely strong structural stability. This result supports the theoretical assumption that liquid EPDM participates in the crosslinking reaction. Because the liquid EPDM molecular chains are firmly grafted onto the three-dimensional crosslinking network via covalent bonds, they cannot undergo physical displacement at high temperatures, thus maintaining the integrity of the internal plasticizing system. Simultaneously, the ion cluster network formed by ZDMA exhibits good thermal stability during aging, effectively suppressing excessive post-crosslinking and oxidative breakage of the main chain, resulting in a tensile strength change rate of only +2.0%. This excellent anti-migration and anti-aging performance ensures that the sealing gasket can maintain the designed elastic compressive stress for a long time in complex underground water conditions and fluctuating temperatures, providing crucial technical support for achieving the goal of long-term service in underground engineering.

[0174] Test Example 6:

[0175] The experimental steps are as follows:

[0176] (1) Standard cylindrical specimens (compliant with ISO 3384 standard type A specimens) with a diameter of 13.0 mm and a thickness of 6.3 mm were cut from the vulcanized rubber sheets of Example 1, Comparative Example 1 and Comparative Example 2. The specimens were placed in a specially designed compressive stress relaxation fixture equipped with a high-precision force sensor that can monitor the changes in sealing reaction force in real time.

[0177] (2) Adjust the clamp bolts to compress the sample to 75% of its initial height (i.e., the compression rate is 25%) and record the initial reaction force value F0 at this time. In order to truly simulate the stress state on the engineering site, this test directly uses the force value read immediately after compression as F0, without deducting the force value attenuation in the early stage of physical relaxation.

[0178] (3) The entire fixture containing the sample was placed in a high-temperature aging chamber at 100°C to simulate the stress state of the shield tunnel joint under long-term service and geothermal environment.

[0179] (4) The sealing reaction force F is continuously recorded through the data acquisition system at logarithmic time intervals (1h, 4h...) and linear time intervals (24h, 48h...168h). t .

[0180] (5) The experiment was stopped after 168 hours, and the stress retention rate R(t) at each time point was calculated. t / F0)×100%. This indicator directly reflects the gasket's ability to resist stress decay and maintain contact pressure under long-term pressure.

[0181] The experimental results are shown in Table 6.

[0182] Table 6. Compressive stress relaxation data (F) of Example 1 and Comparative Examples 1-2 at 100°C t / F0):

[0183]

[0184] Compressive stress relaxation (CSR) is the most critical indicator for evaluating the long-term waterproof reliability of tunnel segment gaskets. It directly simulates the reaction force attenuation process of the gasket under pressure at the segment joints. Table 6 and Figure 4 The data revealed significant differences among the three different micro-network structures under long-term thermo-mechanical coupling.

[0185] Example 1 exhibited satisfactory stress retention capability, maintaining 85.80% of its initial sealing reaction force after 168 hours of high-temperature compression. This excellent performance is attributed to its unique dual-network locking effect. On the one hand, the CC covalent backbone constructed by the peroxide provides stable elastic recovery force, limiting the macroscopic slippage of the molecular chains. On the other hand, the ZDMA ion clusters under MSD regulation act as dynamic crosslinking points. Although they undergo local dissociation under stress to dissipate internal stress, due to the restraint of the liquid EPDM grafted segments, these ion clusters do not undergo long-range migration but recombine at new equilibrium positions. This microscopic dissociation-recombination mechanism effectively alleviates internal stress concentration without causing macroscopic plastic rheology, thus ensuring the durability of the sealing reaction force.

[0186] Conversely, the stress relaxation curve of Comparative Example 1 showed a sharp downward trend, eventually falling below the 50% failure threshold, reaching only 48.50%. This is not only due to the physical relaxation of the rubber molecular chains, but more importantly, to the precipitation of paraffin oil. As small-molecule plasticizers are extruded and volatilized from the pressure-bearing contact surface, the effective volume of the gasket shrinks, leading to a sharp loss of pressure at the contact surface. This physical relaxation caused by material loss is irreversible.

[0187] While Comparative Example 2 did not exhibit the small molecule migration problem, its retention rate was only 59.40%. This is because, in the absence of MSD regulation, the coarse, rigid particles formed by ZDMA self-polymerization exhibit weak interfacial bonding with the rubber matrix. Under constant compressive stress, the rubber molecular chains surrounding these rigid particles are prone to creep and slippage, leading to gradual relaxation of the network structure. This comparative result demonstrates that only by constructing a uniform, stable, and chemically anchored cross-linked network can the problem of excessively rapid stress relaxation in traditional sealing materials be fundamentally solved, thus meeting the stringent requirements for high-durability waterproofing in underground engineering.

[0188] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-resilience, compression-resistant shield tunnel segment sealing gasket, characterized in that, Made from the following ingredients in parts by weight: 100 parts of solid ethylene-propylene-diolefin copolymer; 65-71 parts of reactive predispersed masterbatch; Carbon black 32.5–35 parts; 4-6 parts zinc oxide; Stearic acid 0.5–1.5 parts; Anti-aging agent 2-3 parts; Peroxide vulcanizing agent 4.5–6.5 parts; The reactive predispersed masterbatch is made from the following components in parts by weight: 22.5-25 parts carbon black, 18-30 parts zinc methacrylate, 15-22 parts liquid ethylene propylene diene monomer (EPDM) rubber, and 1.0-1.2 parts α-methylstyrene dimer. The third monomer of the solid ethylene-propylene-diolefin copolymer is 5-ethylidene-2-norbornene, with an ethylene content of 65wt% to 75wt%, a 5-ethylidene-2-norbornene content of 4.5wt% to 5.5wt%, and a Mooney viscosity ML(1+4) of 70 to 90 at 125°C. The liquid EPDM rubber has a number-average molecular weight of 4000-7000 Da, a Brookfield viscosity of 100-500 Pa·s at 50℃, and an iodine value of 10-20 g / 100g. The particle size D50 of the zinc methacrylate is less than 10 μm; The shield tunnel segment sealing gasket is prepared by a method including the following steps: Step (1), preparation of reactive predispersed masterbatch: put carbon black and zinc methacrylate into a mixer and dry mix to obtain a mixed powder; premix liquid EPDM rubber and α-methylstyrene dimer to prepare a mixed liquid; spray the mixed liquid into the mixed powder, and stir under the condition of controlling the material temperature below 70°C until the material is transformed into particles without free liquid to obtain reactive predispersed masterbatch; Step (2), first stage of mixing: Solid ethylene-propylene-diolefin copolymer, zinc oxide, stearic acid, antioxidant and carbon black are put into a mixer for mixing, and then the reactive pre-dispersed masterbatch obtained in step (1) is added and mixed. When the discharge temperature reaches 145℃~150℃, the glue is discharged to obtain the first stage of mixed rubber. Step (3), second-stage vulcanization: the first-stage compound is rolled on a two-roll mill, peroxide vulcanizing agent is added, and after being mixed evenly, it is sheeted out and left to stand; Step (4), vulcanization molding: The rubber compound after being left to stand is vulcanized under high temperature and high pressure.

2. The high-resilience, compression-resistant shield tunnel segment sealing gasket according to claim 1, characterized in that, The peroxide sulfiding agent is bis(tert-butylperoxyisopropyl)benzene; the carbon black is fast-pressing furnace black N550; the chemical name of the α-methylstyrene dimer is 2,4-diphenyl-4-methyl-1-pentene.

3. The high-resilience, compression-resistant shield tunnel segment sealing gasket according to claim 1, characterized in that, The antioxidant is a mixture of antioxidant RD and antioxidant MB.

4. The high-resilience, compression-resistant shield tunnel segment sealing gasket according to claim 1, characterized in that, In step (1): The dry mixing speed is 500-600 rpm, and the time is 1-2 minutes; Increase the speed to 1000-1200 rpm when spraying the mixture, and keep stirring for 3-5 minutes.

5. The high-resilience, compression-resistant shield tunnel segment sealing gasket according to claim 1, characterized in that, In step (2): The initial temperature of the internal mixer is set to 50℃, and the rotation speed is set to 60rpm. First, add solid ethylene-propylene-diolefin copolymer and mix for 60 seconds. Then add zinc oxide, stearic acid, antioxidant and carbon black and continue mixing for 90 seconds. Finally, add reactive predispersed masterbatch and mix for 180 seconds.

6. The high-resilience, compression-resistant shield tunnel segment sealing gasket according to claim 1, characterized in that, In step (3): The roll temperature of the open mill is controlled at 50℃~60℃; The process of mixing evenly includes cutting with the left and right blades three times each and making triangular clumps five times; The film will be stored for 24 hours after it is produced.

7. The high-resilience, compression-resistant shield tunnel segment sealing gasket according to claim 1, characterized in that, In step (4): The vulcanization temperature is 170℃, the pressure is 15MPa, and the time is 10-12 minutes.

8. The high-resilience, compression-resistant shield tunnel segment sealing gasket according to claim 1, characterized in that, In step (1): The reactive predispersed masterbatch is in the form of loose granules without free liquid, wherein liquid EPDM rubber is adsorbed into the pores of carbon black.

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