High-performance, flame-retardant water-based shield tail sealing grease, preparation method and application thereof

Abstract

This invention relates to the field of sealing grease technology, and more particularly to a high-performance, flame-retardant water-based shield tail sealing grease, its preparation method, and its application. The sealing grease comprises, by mass percentage: 10%–25% polyalphaolefin, 15%–30% polyisobutylene, 10%–25% sodium poly(isobutylene-alt-succinate), 10%–18% deionized water, 20%–30% filler, 1%–15% thickener, and 1%–3% reinforcing fibers. Specifically, the polyalphaolefin and polyisobutylene constitute a continuous oil phase, while the sodium poly(isobutylene-alt-succinate) dissolves or disperses in the deionized water and accumulates at the oil-water interface, allowing the deionized water to be stably dispersed as an internal phase, forming a water-in-oil structure. The sealing grease of this invention has moderate zero-point penetration, excellent pumpability, reliable sealing under 3.5MPa water pressure, good erosion resistance under both fresh and seawater conditions, and an ignition point of not less than 295℃. It also has excellent flame retardancy and environmental friendliness, and is suitable for shield tail sealing in long-distance, deep-buried and high-water-pressure shield tunnel construction.

Description

Technical Field

[0001] This invention relates to the field of sealing grease technology, and in particular to a high-performance, flame-retardant water-based shield tail sealing grease, its preparation method, and its application. Background Technology

[0002] Shield tunneling, as the mainstream construction method for urban rail transit, municipal tunnels, and cross-river and cross-sea passages, relies on shield machines to achieve fully mechanized tunneling under conditions of high underground water pressure, weak surrounding rock, and complex strata. During the tunneling process, a circumferential gap inevitably exists between the shield tail and the tunnel segments. If this gap cannot be reliably sealed, groundwater, mud, and sand will flow into the machine, causing a deterioration of the construction environment and even triggering water inrush or mud inrush accidents. To address this, multiple wire brushes are typically installed at the shield tail, and a continuous sealing layer is formed by injecting shield tail sealant to achieve functions such as water stopping, mud prevention, lubrication, and corrosion prevention. The pumpability, penetration, water pressure sealing performance, water erosion resistance, and long-term stability of the shield tail sealant directly affect the safety and economy of shield tunneling construction.

[0003] Early shield tail sealing greases were mostly based on mineral oil, combined with powdered fillers, thickeners, tackifiers, and fiber reinforcement materials to form a paste-like system. For example, patent CN103937590B disclosed a shield tail sealing grease for tunnel boring machines, composed of 15%–25% base oil, 20%–30% powdered fillers, 8%–15% thickener, 2%–8% tackifier, 0.5%–5% dispersant, 16%–33% water-resistant sealing material, and 0.1%–3% antistatic agent, which can, to a certain extent, balance water pressure resistance and pumpability. However, this type of formulation is still mainly based on mineral oil, and the base oil and tackifier polymers are mostly difficult to degrade or non-renewable resources with relatively low flash points. Under high temperature and high water pressure environments, it suffers from insufficient flame retardant properties and difficulty in degradation after leakage.

[0004] To improve environmental friendliness, existing technologies have explored the introduction of bio-based or environmentally friendly base oils. For example, patent CN108865372B proposes an environmentally friendly shield tail sealing grease that uses isooctanol-modified rapeseed oil and soybean oil or biodiesel as the base oil composition, combined with viscosity index modifiers such as polymethyl methacrylate, waterproof sealing materials, and mineral / plant composite fibers to improve biodegradability while maintaining pumpability and sealing performance. Patent CN114214102B uses dimer acid and its derivatives as grease components, combined with aliphatic polyester thickeners and inorganic fillers, to obtain a bio-based shield tail sealing grease with good temperature resistance, pumpability, and water resistance. Such technologies have positive implications for reducing mineral oil usage and improving biosafety, but the overall system is still a pure oil phase system. Flame retardancy mainly relies on high flash point greases and fillers. Under long-distance, deep-buried, or high-water-pressure conditions, the flammability of the grease itself is still difficult to completely avoid. At the same time, while maintaining high water pressure resistance and sealing performance, high-viscosity oily systems are prone to problems such as increased pumping energy consumption and difficulty in low-temperature start-up.

[0005] Some technologies introduce synthetic polymers from the perspective of "balancing environmental protection and sealing performance." For example, the environmentally friendly shield tail sealing grease published in patent CN102925260A significantly improves water pressure resistance, sealing performance, and pumpability through a combination of base oil, viscosity index improver, lubricant, natural biodegradable fiber, filler particulate material, and 0.5 to 3 parts synthetic polymer, and is also environmentally friendly. However, this type of technology also uses the oil phase as the continuous phase, and the synthetic polymer mainly plays a role in thickening and structural reinforcement. It does not utilize the inherent flame-retardant properties of the aqueous phase to systematically design an integrated flame-retardant and sealing structure, making it difficult to fundamentally alleviate the combustion safety risks brought about by the large-scale use of shield tail sealing grease.

[0006] To address the issues of mineral oil systems being difficult to degrade and highly flammable, water-based shield tail sealant solutions with water as the main continuous phase have emerged in recent years. Patent CN113956913A discloses a water-based shield tail sealant whose raw materials include 3-25 parts water, 10-40 parts polypropylene carbonate tackifier, 1-8 parts thickener, and 10-20 parts propylene glycol / glycerol / polyethylene glycol lubricant, with optional addition of fibers and fillers. This system uses water as a solvent, and the polypropylene carbonate derivative achieves both lubrication and tackification, resulting in good overall pumpability and water pressure resistance sealing performance, with significantly reduced toxicity and environmental impact. However, when water is used as the continuous phase, a high water content is usually required to ensure rheological properties and sealing performance. Under high water pressure, seawater scouring, or temperature fluctuations, problems such as water phase seepage, insufficient structural strength, and the risk of low-temperature freezing can easily occur. Furthermore, the introduction of a large amount of hydrophilic components may weaken oil film lubrication and the long-term residence capacity of the oil phase between brush filaments.

[0007] On the other hand, in the fields of lubricating oils, drilling fluids, and emulsion explosives, polyisobutylene-succinic anhydride (PIBSA) and its derivatives have been widely studied and applied as polymeric emulsifiers or ashless dispersants. For example, patent CN110862471A discloses a method for synthesizing a polyisobutylene succinic anhydride polymeric emulsifier for emulsion explosives. This method utilizes the addition reaction of polyisobutylene with maleic anhydride to obtain polyisobutylene succinic anhydride, which is then further esterified to obtain a polymeric emulsifier with excellent emulsifying properties, used to form a stable water-in-oil emulsion explosive system. These works demonstrate that polymers with a polyisobutylene-succinic anhydride backbone exhibit excellent emulsifying, dispersing, and interfacial strengthening effects at the oil-water interface. However, in existing shield tail sealing grease technology, there is no example of introducing such poly(isobutylene-alt-succinic acid) salt polymers into shield tail sealing grease as an interface structure control unit to build a stable oil-in-water structure under low water content conditions, so as to simultaneously utilize the flame retardancy of the internal water phase and the sealing and lubrication advantages of the external oil phase.

[0008] In summary, among existing technologies: 1) Traditional mineral oil or bio-based grease-based shield tail sealants (such as CN103937590B, CN108865372B, CN114214102B) perform well in terms of water pressure resistance and sealing performance and construction adaptability, but their overall flammability is relatively high, and they pose fire safety hazards and environmental accumulation problems in long-distance, deep-buried, high-water-pressure, and seawater environments; 2) Water-based shield tail sealant solutions (such as CN113956913A) improve flame retardancy and environmental friendliness by increasing water content, but the water as a continuous phase still has insufficient resistance to water erosion, low-temperature adaptability, and structural stability under high water pressure conditions; 3) The application of synthetic polymers in shield tail sealants is mostly limited to viscosity adjustment or general structural enhancement, with insufficient fine design of the microstructure of the oil-water interface, and the contradiction of "increasing water content is required to improve flame retardancy, while limiting water content is required for water sealing and structural stability" has not yet been resolved.

[0009] Therefore, there is an urgent need to propose a water-based shield tail sealing grease that, within the framework of polyalphaolefin / polyisobutylene oil phase, precisely regulates the oil-water interface through interfacially active polymers, so that a limited amount of water is stably dispersed as an internal phase, thereby constructing a stable oil-in-water structure. This grease should simultaneously achieve high flame retardancy, high water tightness, good pumpability, and environmental friendliness at a low water content, in order to meet the higher requirements of shield tail sealing materials in complex geological and high water pressure shield tunneling projects. Summary of the Invention

[0010] The technical objective of this invention is to provide a water-based shield tail sealing grease with a stable oil-in-water structure, using polyalphaolefin / polyisobutylene as the oil phase and introducing sodium poly(isobutylene-alt-succinate) to construct a stable water-in-oil structure, given the increasing demands for pumpability, water pressure resistance, and environmental friendliness of existing shield tail sealing greases. This allows a limited amount of deionized water in the system to play a role in flame retardancy and environmental protection without compromising the sealing grease's water tightness, resistance to water / seawater erosion, and suitable cone penetration. This satisfies the demand for high-performance, flame-retardant, and environmentally friendly shield tail sealing materials in long-distance, deep-buried, and high-water-pressure shield tunneling projects.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: A high-performance, flame-retardant water-based shield tail sealant, comprising the following components by weight percentage: Polyalphaolefin: 10%–25%; Polyisobutylene: 15%–30%; Sodium poly(isobutylene-alt-succinate): 10%–25%; Deionized water: 10%–18%; Filler: 20%–30%; Thickener: 1%–15%; Reinforcing fiber: 1%–3%; In this process, the polyalphaolefin and the polyisobutylene together constitute a continuous oil phase, and the sodium poly(isobutylene-alt-succinate) is dissolved or dispersed in the deionized water and distributed at the interface between the oil phase and the water phase, so that the deionized water is dispersed as an internal phase with a mass fraction of 10% to 18%, thereby forming a stable water-in-oil structure.

[0012] Preferably, the sealant comprises the following components by weight percentage: Polyalphaolefin: 15%–20%; Polyisobutylene: 20%–25%; Sodium poly(isobutylene-alt-succinate): 15%–20%; Deionized water: 12%–16%; Filler: 22%–28%; Thickener: 2%–10%; Reinforcing fiber: 1.5%–2.5%.

[0013] Preferably, the polyalphaolefin is a non-metallocene polyalphaolefin and / or a metallocene polyalphaolefin.

[0014] Preferably, the polyisobutylene is polyisobutylene with a number average molecular weight of 800 to 2000.

[0015] Preferably, the filler is selected from one or more combinations of talc powder, mica powder, kaolin, slag powder, wood flour, calcium carbonate, magnesium carbonate, and barium sulfate. The filler is mainly used to adjust hardness and water washability, improve the wear resistance of the sealant, and optimize costs.

[0016] Preferably, the thickener is selected from at least one of silica, organobentonite, starch resin, tannin, and grafted starch.

[0017] Preferably, the reinforcing fiber is selected from at least one of natural fibers, synthetic fibers, and mineral fibers. Natural fibers are preferred. Using natural fibers as the reinforcing fiber ensures that the fiber is environmentally friendly and harmless, while maintaining the sealed tensile strength and sealing performance.

[0018] As a further preferred option, the polyalphaolefin is a metallocene polyalphaolefin with a kinematic viscosity at 100°C ≥2000 cst.

[0019] As a further preferred option, the polyisobutylene is polyisobutylene with a number average molecular weight of 1000 to 1800.

[0020] As a further preferred option, the mass ratio of sodium poly(isobutylene-alt-succinate) to deionized water is 0.15:1 to 0.30:1; As a further preferred option, the filler is selected from a combination of calcium carbonate and barium sulfate, wherein the mass fraction of calcium carbonate is 20-25% and the mass fraction of barium sulfate is 2-5%.

[0021] As a further preferred option, the thickener is selected from silica, and the mass fraction of silica is 8-12%.

[0022] As a further preferred option, the reinforcing fiber is a natural fiber, selected from one or more of wood fiber, cotton fiber, flax fiber, bamboo fiber, and hemp fiber. The synthetic fiber includes, but is not limited to, polyester fiber, acrylic fiber, polypropylene fiber, and polypropylene fiber; the mineral fiber includes, but is not limited to, glass fiber, quartz fiber, sepiolite fiber, and asbestos fiber.

[0023] Specifically, the polyalphaolefin is selected from at least one of mPAO2000, mPAO5500, mPAO10000 and mPAO20000; and / or, the polyisobutylene is polyisobutylene with a number average molecular weight of 1300; and / or, the reinforcing fiber is selected from cotton fiber, and the mass fraction of the reinforcing fiber is 1.0 to 2.0%.

[0024] As a further preferred option, the sodium poly(isobutylene-alt-succinic acid) has a molecular weight of 300,000 to 350,000.

[0025] Furthermore, the present invention also provides a method for preparing the aforementioned high-performance, flame-retardant water-based shield tail sealant, comprising the following steps: 1) Oil phase premixing: Polyalphaolefin and polyisobutylene are added to a premixing vessel and heated to 80-90°C under stirring to obtain a uniformly mixed oil phase; 2) Preparation of aqueous phase and emulsion system: Sodium poly(isobutylene-alt-succinate) is added to deionized water and stirred to dissolve or disperse in the range of room temperature to 60°C to obtain a uniform aqueous emulsion; 3) Emulsification and dispersion: Under the condition of maintaining the oil phase temperature at 80-90℃, the aqueous emulsion obtained in step 2) is slowly added to the oil phase obtained in step 1) under stirring or shearing conditions, so that the deionized water is uniformly dispersed in the oil phase under the action of sodium poly(isobutylene-alt-succinate) to form a stable water-in-oil emulsion. 4) Meshing and mixing: Transfer the water-in-oil emulsion material obtained in step 3) to the meshing machine, adjust the material temperature to 80-90℃, and add filler, thickener and reinforcing fiber in sequence under meshing conditions. After each addition, continue meshing for 20-30 minutes until the material is uniform, and the high-performance, flame-retardant water-based shield tail sealant is obtained.

[0026] Step 2) The mass fraction of sodium poly(isobutylene-alt-succinate) in deionized water is 10% to 25%, and the mixture is stirred for 10 to 60 minutes at a shear speed of ≥500 rpm to ensure complete dissolution or dispersion. And / or, in step 3), the time for adding the aqueous emulsion to the oil phase is controlled within 10 to 60 minutes, and a mechanical stirring or high shear dispersion device with a rotation speed of 500 to 2000 rpm is used to form a stable water-in-oil structure. And / or, in step 4), the total engagement time is 60 to 120 minutes, and the material temperature is controlled at 70 to 90°C at the end of engagement, so as to obtain a paste-like sealing grease with a zero-thrust depth of 220 to 250.

[0027] Furthermore, the present invention also provides a method for sealing the tail of a tunnel boring machine, using the aforementioned high-performance, flame-retardant water-based tail sealing grease. The sealing grease is continuously injected into the space between the wire brushes of the tail of the tunnel boring machine using a grease injection pump, so that the sealing grease fills the interior of the wire brushes and the gaps between the wire brushes to form a sealing layer. The pumping rate of the sealing grease is not less than 40 g / min under the conditions of 1 MPa and 25°C, and it remains water-proof under a water pressure of 3.5 MPa.

[0028] Preferably, the tunnel boring machine is used for long-distance, deep-buried or high-water-pressure tunnel construction, the sealing layer passes the water erosion resistance test and seawater erosion test at 38°C, and the ignition point of the sealing grease is not lower than 295°C in the construction environment.

[0029] This invention introduces sodium poly(isobutylene-alt-succinate) with a specific molecular weight and dosage range into a polyalphaolefin / polyisobutylene oil phase system, enabling it to form a dense and viscoelastic polymeric interfacial film at the oil-water interface. Under limited water content conditions of 10%–18%, a stable water-in-oil structure is constructed, achieving a synergistic improvement in flame retardancy and water tightness. On the one hand, the inner deionized water phase significantly increases the ignition point of the system; the ignition point of the sealing grease is not lower than 295°C under construction conditions, effectively reducing the risk of combustion at the shield tail area due to high temperature and ignition sources. On the other hand, the outer high-viscosity mPAO / PIB oil phase, combined with calcium carbonate / barium sulfate, etc. The filler and natural fiber skeleton endow the sealant with excellent water pressure sealing ability and erosion stability. It does not leak water under 3.5MPa water pressure, passes the water erosion test and seawater washout test at 38℃, and the zero-time cone penetration is stable in the range of 220-250. The pumping rate is not less than 40g / min at 1MPa and 25℃. It ensures moderate resistance during the grease injection process, can be transported over long distances, and maintains good residence and anti-creep performance between the shield tail wire brushes. Compared with traditional pure oil-based shield tail grease, this invention significantly improves flame retardant safety and environmental friendliness while maintaining or even optimizing water tightness, pumpability and long-term sealing reliability. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0031] I. Raw Materials and Terminology 1. Polyalphaolefin (PAO) The polyalphaolefin used in this invention is a synthetic base oil, preferably metallocene polyalphaolefin (mPAO), and more preferably a high-viscosity variety with a kinematic viscosity of not less than 2000 cSt at 100°C, such as commercially available mPAO2000, mPAO5500, mPAO10000, and mPAO20000. As an important component of the continuous oil phase, mPAO, together with polyisobutylene, constructs a high-viscosity oil phase framework, giving the sealing grease good adhesion, shear resistance, and high-temperature resistance. When forming a water-in-oil structure, it effectively encapsulates and blocks the internal water phase, which is one of the keys to ensuring the synergistic effect of watertightness and flame retardancy.

[0032] 2. Polyisobutylene (PIB) Polyisobutylene (PIB) is a commonly used high-viscosity thickener and thickener, with a preferred relative molecular mass of 800–2000. In this embodiment, PIB1300 with a number-average molecular mass of approximately 1300 is preferred. PIB and mPAO form a composite oil phase, which on the one hand improves the adhesion and bridging ability of the sealing grease to the tail wire brush and segment concrete, enhancing its resistance to creep and vibration loss; on the other hand, it synergizes with the interfacial polymers and filler network to stabilize the water-in-oil emulsion droplet structure, improving oil film retention and water erosion resistance.

[0033] 3. Sodium poly(isobutylene-alt-succinate) (PIB-alt-MA-Na) Sodium poly(isobutylene-alt-succinate) is an anionic polymeric polyelectrolyte obtained by ring-opening and neutralization of polyisobutylene and maleic anhydride. Its main chain contains hydrophobic polyisobutylene segments, and its side groups contain multiple carboxyl groups. This invention preferably uses high molecular weight varieties with a number average molecular weight of 300,000 to 350,000 to ensure the formation of a continuous, dense, and viscoelastic polymeric "shell" at the oil-water interface. The sodium poly(isobutylene-alt-succinate) of this invention can be selected from the ISOBAM series products manufactured by Kuraray Co., Ltd., with ISOBAM-18 being particularly suitable.

[0034] In this invention, sodium poly(isobutylene-alt-succinate) is first dissolved or dispersed in deionized water to form an aqueous emulsion, and then dispersed into a continuous oil phase of mPAO / PIB under high temperature and high shear conditions. Part of this polymer dissolves in the aqueous phase, while a portion accumulates at the oil-water interface, forming a thick-shell micelle or droplet shell. This shell is held in the oil phase by hydrophobic-hydrophobic interactions, while simultaneously forming a strong hydration layer with the aqueous phase using anionic groups. This significantly improves the interfacial strength and anti-agglomeration ability of the water droplets, making it the core interfacial unit for constructing a stable water-in-oil structure.

[0035] 4. Deionized water Deionized water is one of the main sources of the "water-based" and "flame-retardant" properties of this invention. Unlike traditional completely dehydrated greases, this invention retains 10-18% by mass of deionized water, and through a polymer shell formed by sodium poly(isobutylene-alt-succinate) at the oil-water interface, the water is stably dispersed into micron- or submicron-sized internal phase droplets, allowing the water to exist in the system for a long time without easily precipitating out. Water itself has high specific heat and non-flammability, which can significantly improve the ignition point and fire resistance of the sealing grease. At the same time, the internal phase water is encapsulated by the oil phase and the polymer interface layer, and will not directly damage the oil film and sealing structure.

[0036] 5. Packing material Fillers are used to adjust the density, hardness, and abrasion resistance of the sealing grease, and to improve its resistance to water erosion. Optional fillers include one or more of talc, mica powder, kaolin, slag powder, wood flour, calcium carbonate, magnesium carbonate, and barium sulfate. A preferred combination is calcium carbonate and barium sulfate, with calcium carbonate typically comprising 20–25% by mass and barium sulfate typically comprising 2–5% by mass. Calcium carbonate provides the basic framework and thixotropic support, while barium sulfate, with its higher density, helps improve the grease's resistance to erosion and its "staying place" in the tail space.

[0037] 6. Thickener Thickeners are used to further enhance the three-dimensional network structure and thixotropy of the system, preventing structural collapse under high temperature or high shear conditions. The thickener in this invention can be selected from at least one of precipitated silica, organobentonite, starch resin, tannin, and grafted starch, with precipitated silica being preferred. Precipitated silica has characteristics such as large specific surface area, high surface activity, and both lipophilic and hydrophilic groups, enabling it to form multi-point hydrogen bonds or electrostatic interactions with the mPAO / PIB oil phase, the sodium poly(isobutylene-alt-succinate) interface layer, and the aqueous phase, significantly improving colloidal stability and anti-flowing ability.

[0038] 7. Reinforcing fibers The reinforcing fibers are mainly used to improve the tensile strength, bridging ability, and erosion resistance of the sealing grease between the tail wire brushes, while also having a significant impact on creep performance and holding force under vibration conditions. This invention preferably uses natural fibers, such as wood fibers, cotton fibers, flax fibers, bamboo fibers, and hemp fibers, but synthetic fibers or mineral fibers can also be used. However, it is preferred that the material includes at least a certain proportion of natural fibers to improve its biodegradability and environmental friendliness. In this embodiment, cotton fibers are typically used, with a mass fraction of 1.0% to 2.0%.

[0039] Those skilled in the art may also add small amounts of antifungal agents, preservatives, antioxidants, and other auxiliary components as needed. As long as the oil-polymer-water ternary structure and its corresponding performance balance emphasized in this invention are not disrupted, such adjustments are within the scope of protection of this invention.

[0040] II. Formulation and Structural Mechanism of the Invention The core of this invention, a high-performance, flame-retardant water-based shield tail sealant, lies in the introduction of sodium poly(isobutylene-alt-succinate) with a specific molecular weight and dosage range into a continuous oil phase of polyalphaolefin / polyisobutylene, while retaining 10-18% by mass of deionized water, so that these three components can construct a stable "oil-polymer-water" ternary equilibrium system.

[0041] Specifically, mPAO and PIB form a high-viscosity continuous oil phase, providing basic lubrication and a sealing framework; deionized water is dispersed into a large number of fine internal phase water droplets under the emulsification and interfacial stabilization of sodium poly(isobutylene-alt-succinate); sodium poly(isobutylene-alt-succinate) dissolves / disperses in the aqueous phase and accumulates at the oil-water interface, forming a polymer shell with a certain thickness and viscoelasticity, embedding the hydrophobic polyisobutylene backbone into the oil phase and extending the hydrophilic carboxylate groups into the aqueous phase, thereby significantly improving the interfacial tension and anti-coagulation ability of the internal phase water.

[0042] This water-in-oil structure brings about the following synergistic effect: 1. Enhanced flame retardancy: Water droplets are evenly dispersed in the oil phase, which is equivalent to arranging a large number of "micro-cooling / extinguishing points" inside the oil film. Under the action of external heat source, water absorbs heat and inhibits the temperature rise of the oil phase, effectively increasing the ignition point of the entire system. 2. Water tightness and erosion resistance: The continuous oil phase is composed of high-viscosity mPAO / PIB, supplemented by a three-dimensional network constructed with calcium carbonate, barium sulfate, silica and fibers, which "encapsulates and locks" the internal phase water, preventing external high-pressure water from penetrating into the interior and preventing the internal water from being lost rapidly during erosion, thus maintaining extremely low mass loss even under high water pressure and seawater environments. 3. Rheology and pumping balance: The presence of the sodium poly(isobutylene-alt-succinate)-water internal phase reduces the viscosity of the pure oil phase system to a certain extent, keeping the zero cone penetration within the range of 220-250, which is beneficial for smooth pumping under 1MPa conditions; at the same time, the oil phase, filler, and fiber network ensure the formation of a stable "bridging and filling" structure between the shield tail wire brushes, avoiding sagging and severe creep during construction.

[0043] Compared with traditional "fully oil-phase" shield tail sealant, this invention significantly improves flame retardant safety and environmental friendliness while maintaining or improving water tightness and pumpability. Compared with water-based systems with water as the continuous phase, this invention avoids the low-temperature risk and water tightness reduction caused by high water content through the structural design of "oil phase on the outside and water phase on the inside", and achieves a balance between flame retardancy and high water pressure sealing performance.

[0044] III. General Steps of the Preparation Method The preparation method of the high-performance, flame-retardant water-based shield tail sealant of the present invention mainly includes the following steps, corresponding to the contents described in claims 7-8: 1. Oil phase premixing Add a predetermined mass of polyalphaolefin (e.g., mPAO2000) and polyisobutylene to a premixing vessel equipped with a heating and stirring device. Start stirring and slowly heat the system to 80–90°C using jacketed hot oil or electric heating. Continue stirring within this temperature range for 10–30 minutes to ensure complete mixing of mPAO and PIB, forming a uniform, transparent or semi-transparent high-viscosity oil phase.

[0045] 2. Preparation of aqueous phase and emulsion system Sodium poly(isobutylene-alt-succinate) is added to deionized water according to the mass ratios specified in claims 1 to 4, and dissolved or dispersed under stirring at room temperature to 60°C. Preferably, the mass fraction of sodium poly(isobutylene-alt-succinate) in the aqueous phase is 10% to 25%, and the stirring or shearing speed is not less than 500 rpm for 10 to 60 minutes to ensure that the polymer is fully hydrated and forms a homogeneous aqueous emulsion. The resulting water is a transparent or translucent solution with a certain viscosity.

[0046] 3. Emulsification and dispersion form a water-in-oil system. While maintaining the oil phase temperature at 80–90°C, the aqueous emulsion obtained in step 2) is slowly added to the oil phase at a constant flow rate while maintaining medium to high intensity stirring or connecting a high-shear dispersing head. The addition time of the aqueous phase is preferably controlled within 10–60 minutes, and the stirring or shearing speed is preferably 500–2000 rpm. During this process, the aqueous phase is torn into numerous small droplets under the action of sodium poly(isobutylene-alt-succinate). One end of the polymer chain is embedded in the oil phase, and the other end extends into the aqueous phase, forming a stable shell at the oil-water interface. This gradually forms a stable water-in-oil emulsion with the mPAO / PIB oil phase as the continuous phase and water as the internal phase.

[0047] After emulsification, continue stirring for 10–30 minutes to further homogenize the droplet size and achieve a stable state.

[0048] 4. Interlocking and mixing with the addition of fillers, thickeners and fibers The above-mentioned water-in-oil emulsion is transferred to a mixing machine or internal mixer. The material temperature is adjusted to 80-90°C. While in the mixing state, fillers, thickeners, and reinforcing fibers of predetermined types and amounts are added sequentially. Preferably: First, add inorganic fillers such as calcium carbonate and barium sulfate, and let them mesh for 20 to 30 minutes to ensure that they are evenly dispersed and nested with the oil-polymer-water matrix. Add thickeners such as silica and continue meshing for 20-30 minutes to establish a denser spatial network structure. Finally, add reinforcing fibers such as cotton fibers and continue meshing for 20-30 minutes to disperse the fibers into short pieces, which are evenly distributed in the three-dimensional network, thereby enhancing the bridging and erosion resistance of the system.

[0049] The total time for the entire meshing process is typically controlled between 60 and 120 minutes. During the meshing process, the jacket temperature or cooling water flow rate can be adjusted as needed to gradually reduce the material temperature to the range of 70 to 90°C, in order to balance the formation of the network structure and prevent excessive evaporation of moisture. After the meshing is completed, the material is unloaded and allowed to cool naturally or in a cooling tank to room temperature, thus obtaining the high-performance, flame-retardant water-based shield tail sealant of this invention.

[0050] IV. Performance Testing Methods The present invention uses the following indicators and standards to evaluate the performance of sealing grease (in conjunction with the aforementioned technical solutions in the specification): 1. Cone penetration test Zero cone penetration tests were performed according to GB / T269 standard to characterize the consistency, texture, and flowability of the sealing grease. Insufficient cone penetration leads to pumping difficulties, while excessive penetration may cause leakage and seal failure. The target range for this invention is 220–250.

[0051] 2. Volatility test According to ASTM D972 standard, the percentage of mass loss was tested after being placed at 100°C for 24 hours to evaluate the high-temperature storage stability of the sealing grease and the volatilization of light components.

[0052] 3. Water erosion resistance test The test was conducted at 38℃. The sealing grease sample was rolled into a ball approximately 4 cm in diameter, placed in a beaker, and completely submerged in sufficient deionized water. The mixture was stirred with a glass rod at 60 rpm for 5 minutes. After the test, the sample surface was observed for obvious peeling or dispersion. The sample was then removed and gently kneaded in the palm of the hand. If the sample remained firmly adhered to the palm, the paste did not soften or thin significantly, and no excess oil or water was released, the test was considered successful.

[0053] 4. Seawater washout test The method is similar to the water erosion resistance test, but deionized water is replaced with 3.5% NaCl aqueous solution to simulate the erosion resistance performance in a seawater environment.

[0054] 5. Water tightness test According to ASTM D1264, a water tightness test is performed on the sample at 79°C for 1 hour to evaluate the ability of the sealing grease to prevent high-pressure water penetration. The test is characterized by the percentage of mass loss or the amount of leakage, and the required index is usually ≤3%.

[0055] 6. Pumpability Test According to ASTM D1092, the pumping rate of sealing grease is tested at 25°C and 1 MPa for a specified time, and is characterized in g / min. The higher the value, the easier it is to deliver during field grease injection.

[0056] 7. Peristalsis Test According to JISA 5758, the sample is coated onto a vertical metal or glass plate, and the flow distance is observed under specified temperature and time conditions. The anti-creep ability is characterized in mm. The higher the value, the better the anti-slip performance under a certain load. The target value of this invention is generally above 30.

[0057] 8. Oil Stagnation Test According to JISA 5751, the sample is placed on filter paper, and the number or width of the oil spots is measured after a specified time to characterize the tendency of the base oil to separate. The smaller the value, the better the oil's retention. Generally, ≤12 is required.

[0058] 9. Ignition point test According to ASTM D92, the ignition point of sealing grease is determined using the open cup method to evaluate its flame retardant properties. This invention requires an ignition point of not less than 295°C, preferably greater than 300°C.

[0059] In the following examples, unless otherwise specified, the percentage content of each component is a mass percentage, and the preparation process is generally carried out according to the above general steps.

[0060] Examples 1-3: Shield Tail Sealing Grease with Different Water Contents and Interfacial Polymer Amounts The formulations of Examples 1 to 3 are shown in Table 1. The main difference lies in the different contents of deionized water and sodium poly(isobutylene-alt-succinate).

[0061] Table 1 Formulations of Examples 1-3

[0062] Example of preparation steps (represented by Example 2): Add 18 parts of mPAO2000 and 20 parts of PIB1300 to a premixing vessel, heat to 85°C, and stir for 20 minutes to obtain a homogeneous oil phase. Add 16 parts of sodium poly(isobutylene-alt-succinate) to 14 parts of deionized water and stir at 50°C and 800 rpm for 30 min to obtain a uniform, slightly viscous aqueous emulsion. Maintain the oil phase temperature at 85℃, and slowly add the aqueous emulsion to the oil phase over 30 minutes with a stirring intensity of 1000 rpm. Continue stirring for 20 minutes to form a stable water-in-oil emulsion. Transfer the emulsion material to the meshing machine, keep the material temperature at about 85°C, and add 19 parts calcium carbonate, 3 parts barium sulfate, 8 parts silica and 2 parts cotton fiber in sequence. After each addition, mesh for 20 to 30 minutes, with a total meshing time of about 90 minutes. Gradually cool down to about 75°C during the process. The material was unloaded and allowed to cool naturally to room temperature to obtain the sealing grease of Example 2. Examples 1 and 3 only had the proportions of each raw material adjusted according to the ratios in Table 1, and the preparation process was the same.

[0063] The performance of the sealing greases prepared in Examples 1-3 was tested, and the results are shown in Table 2.

[0064] Table 2 Test Results of Examples 1-3

[0065] As shown in Table 2, with the gradual increase in the content of deionized water and sodium poly(isobutylene-alt-succinate) from Example 1 to Example 3, the ignition point of the sealing grease increased from 305°C to 345°C, demonstrating that a limited aqueous phase can significantly improve flame retardancy under the protection of a polymer interface layer. Simultaneously, the water tightness test showed an increase from 0.3% to 2.0%, still meeting the requirement of ≤3%, indicating that within the recommended range of this invention, the increase in water content has a certain impact on water tightness but is still acceptable. Considering both flame retardancy and water tightness, Example 2 achieves a better balance between the two.

[0066] Examples 4-6: Performance Comparison at Different mPAO / PIB Ratios In Examples 4-6, the amounts of sodium poly(isobutylene-alt-succinate), deionized water, filler, thickener, and cotton fiber were kept the same as in Example 2, with only the ratio of mPAO to PIB being adjusted. The formulations are shown in Table 3.

[0067] Table 3 Formulations of Examples 4-6

[0068] The sealing greases prepared in Examples 4-6 were tested, and the results are shown in Table 4.

[0069] Table 4 Test Results of Examples 4-6

[0070] As shown in Table 4, with the continuous increase of mPAO content from Example 4 to Example 6 and the gradual decrease of PIB content, the water tightness decreased from 1.4% to 0.5%, and the ignition point increased from 320℃ to 338℃. This indicates that increasing the high viscosity mPAO is beneficial to improving water pressure resistance and flame retardancy. Meanwhile, the number of penetration points in the oil stagnation test increased from 5 to 11, indicating that the "activity" of the oil increased after increasing the mPAO content, but it was still controlled within the required range. In summary, Examples 2 and 5 achieved a good balance between oil stagnation, pumpability, and flame retardancy.

[0071] VI. Comparative Example To highlight the comprehensive effect of the present invention, which is a "poly(isobutylene-alt-succinic acid) sodium interfacial polymer + water-in-oil structure", the following comparative ratios were set up for comparative verification.

[0072] Comparative Example 1: Conventional non-aqueous PIB + filler system Comparative Example 1 does not introduce deionized water and sodium poly(isobutylene-alt-succinate), but uses a traditional PIB + filler + silica + cotton fiber system, with the following formulation: PIB1300: 37% Calcium carbonate: 37% Barium sulfate: 5% Silica: 18% Cotton fiber: 3%.

[0073] Ordinary shield tail sealing grease was prepared using conventional mixing and meshing processes. Test results showed that the penetration depth was approximately 245 mm in 0 cycles, and the watertightness mass loss at 79°C and 1 hour was approximately 0.8%. It passed both water erosion and seawater washout tests, indicating that the formulation has certain watertightness advantages. However, the ignition point was only about 225°C, which is significantly lower than the 320°C or higher level of Examples 2-6 of this invention, indicating that the flame retardant performance was significantly insufficient.

[0074] Comparative Example 2: Aqueous emulsion system without polymer emulsion Comparative Example 2 retains deionized water but does not introduce sodium poly(isobutylene-alt-succinate). It uses only a simple dispersion system of mPAO / PIB + filler + silica + cotton fiber, with the following formulation: mPAO2000: 18% PIB1300: 22% Deionized water: 14% Calcium carbonate: 21% Barium sulfate: 3% Silica: 20% Cotton fiber: 2%.

[0075] During preparation, vigorous stirring at 80–90°C mechanically dispersed the aqueous phase in the oil phase. However, due to the lack of a polymeric interfacial stabilizer, the water droplets were relatively large and prone to aggregation. In the tests, the zero-point cone penetration was approximately 232, and the ignition point was approximately 300°C, showing some improvement compared to Comparative Example 1. However, the watertightness loss at 79°C and 1 hour reached approximately 7.5%. Significant paste peeling and aqueous phase precipitation were observed in both water erosion and seawater washout tests, indicating that mechanical dispersion alone is insufficient to maintain high watertightness.

[0076] Comparative Example 3: Emulsification system using low molecular weight surfactants In Comparative Example 3, a water-in-oil structure was constructed using the nonionic low-molecular-weight surfactant Tween 80 / Span 80 without the use of sodium poly(isobutylene-alt-succinate), and the polymeric interfacial layer was not established. An example formulation is shown below: mPAO2000: 20% PIB1300: 20% Tween 80: 8.5% Span 80:3% Deionized water: 14% Calcium carbonate: 19% Barium sulfate: 3% Silica: 10% Cotton fiber: 2%.

[0077] The obtained sealing grease had a cone penetration of approximately 226 mm and an ignition point of approximately 310°C. It exhibited high pumpability (>50 g / min) at 1 MPa and 25°C, indicating that the low molecular weight surfactants could form a basic water-in-oil emulsion structure and improve flame retardancy. However, in the water tightness test at 79°C for 1 hour, the mass loss was approximately 6.3%. In the water erosion and seawater washout tests, the emulsion layer was easily sheared and damaged, resulting in water separation, and it could not meet the high water pressure sealing requirements.

[0078] Comparative Example 4: Using other water-soluble polymers (such as sodium polyacrylate) In Comparative Example 4, sodium polyacrylate was used to replace sodium poly(isobutylene-alt-succinate) at a mass fraction of 16%, while the rest of the formulation was similar to that of Example 2. The resulting sealing grease could also form a water-in-oil emulsion structure macroscopically, with a zero cone penetration of about 230° and an ignition point of about 320°, indicating acceptable flame retardant performance. However, due to the complete hydrophilicity of the sodium polyacrylate main chain and the lack of hydrophobic segments embedded in the oil phase, the oil-water interface shell was thin and easily cracked under shear. The water tightness mass loss at 79°C for 1 hour was about 4.5%, slightly higher than the 3% requirement. Local detachment and water phase seepage were observed in the water erosion resistance test, posing a safety hazard for high water pressure shield tail sealing conditions.

[0079] For ease of comparison, the key performance characteristics of Example 2 and Comparative Examples 1-4 are summarized in Table 5.

[0080] Table 5 Performance comparison between Example 2 and Comparative Examples 1-4

[0081] As can be seen from Table 5: 1. Comparative Example 1 is a traditional non-water-based PIB+ filler system. It has good water tightness but an ignition point of only 225℃. Its flame retardant performance is far from meeting the requirements of high-safety shield tunneling projects. 2. Although the introduction of water in Comparative Example 2 increased the ignition point, the lack of a polymer interface layer significantly reduced the water tightness, making it unable to pass the water erosion and seawater washout tests. 3. Comparative Example 3 uses a low-molecular-weight surfactant to form a water-in-oil structure, which has good flame retardancy but the interfacial shell is too thin and lacks strength. It is easily damaged under high water pressure and shear conditions and also cannot meet the watertightness requirements. 4. When Comparative Example 4 is replaced with other water-soluble polymers, although the flame retardancy is acceptable, it is difficult to form a "thick-shell" interface structure similar to that of the present invention due to the lack of hydrophobic segments embedded in the oil phase, and the water tightness still cannot reach the target of ≤3%.

[0082] In contrast, Example 2 of this invention constructs a stable water-in-oil structure by using sodium poly(isobutylene-alt-succinate) with a specific molecular weight and dosage range in conjunction with a continuous oil phase of mPAO / PIB and 12-16% deionized water. While maintaining a cone penetration of 229 and a pumping rate of 49 g / min, the ignition point is increased to 332°C. At the same time, the mass loss in the watertightness test is only 0.8%, and the water erosion resistance and seawater washout tests are passed stably. This fully demonstrates that the technical solution of this invention achieves a comprehensive performance improvement that is difficult to achieve in the prior art between flame retardancy and high water pressure sealing.

[0083] VII. Conclusion A comparison of the above embodiments with the comparative examples shows that: Significantly improved flame retardant performance Traditional non-water-based shield tail sealing greases typically have an ignition point of around 220–260°C, with Comparative Example 1 showing an ignition point of 225°C. This invention, by introducing sodium poly(isobutylene-alt-succinate) into the mPAO / PIB oil phase and stably retaining 10–18% internal water, stably raises the ignition point to 320–345°C, effectively reducing the risk of combustion in the shield tail area caused by frictional heating or external ignition sources.

[0084] 2. High watertightness and erosion resistance The water tightness test results of ordinary aqueous systems (Comparative Example 2), low-molecular-weight surfactant emulsion systems (Comparative Example 3), and other water-soluble polymer systems (Comparative Example 4) at 79°C for 1 hour all showed a mass loss exceeding 3%, failing to meet the high-pressure shield tail sealing requirements. However, in Examples 1-6 of this invention, protected by a thick-shell interface layer constructed from sodium poly(isobutylene-alt-succinate), the water tightness mass loss was less than 2.1%, with Typical Example 2 showing a loss of only 0.8%. Furthermore, both water erosion and seawater runoff tests were passed, demonstrating that this invention exhibits excellent sealing and anti-leakage capabilities in both freshwater and seawater environments.

[0085] 3. Good pumpability and site adaptability The zero-point cone penetration of Examples 1 to 6 of the present invention is all within the range of 221 to 235, and the pumping rate is between 45 and 52 g / min under the conditions of 1 MPa and 25℃. Compared with the "softer system" such as Comparative Example 3, it will not flow excessively, and compared with the "harder system" such as Comparative Example 1, it will not cause pump blockage. It is suitable for the continuous grease injection requirements of long-distance shield tunneling.

[0086] 4. Environmental friendliness and biodegradability advantages This invention selects mPAO / PIB as the high-viscosity oil phase and preferably uses natural fibers such as cotton fiber as the reinforcing phase. Compared with traditional formulations containing large amounts of mineral oil and asbestos fibers, it has better environmental friendliness and potential biodegradability. While ensuring sealing performance and flame retardant performance, it can effectively reduce the long-term environmental burden of the shield tail sealant in the soil.

[0087] In summary, this invention, by introducing sodium poly(isobutylene-alt-succinate) of a specific molecular weight and constructing a stable water-in-oil structure, achieves a comprehensive performance improvement that is difficult to achieve simultaneously with conventional technologies in terms of flame retardancy, watertightness, pumpability, and environmental friendliness. It possesses outstanding substantive features and significant progress. The above is a description of embodiments of this invention. Through the above description of the disclosed embodiments, those skilled in the art will be able to implement or use this invention. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, this invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A high-performance, flame-retardant water-based shield tail sealant, characterized in that, This sealant comprises the following components by weight percentage: Polyalphaolefin: 10%–25%; Polyisobutylene: 15%–30%; Sodium poly(isobutylene-alt-succinate): 10%–25%; Deionized water: 10%–18%; Filler: 20%–30%; Thickener: 1%–15%; Reinforcing fiber: 1%–3%; In this process, the polyalphaolefin and the polyisobutylene together constitute a continuous oil phase, and the sodium poly(isobutylene-alt-succinate) is dissolved or dispersed in the deionized water and distributed at the interface between the oil phase and the water phase, so that the deionized water is dispersed as an internal phase with a mass fraction of 10% to 18%, thereby forming a stable water-in-oil structure.

2. The high-performance, flame-retardant water-based shield tail sealant according to claim 1, characterized in that, This sealant comprises the following components by weight percentage: Polyalphaolefin: 15%–20%; Polyisobutylene: 20%–25%; Sodium poly(isobutylene-alt-succinate): 15%–20%; Deionized water: 12%–16%; Filler: 22%–28%; Thickener: 2%–10%; Reinforcing fiber: 1.5%–2.5%.

3. The high-performance, flame-retardant water-based shield tail sealant according to claim 1, characterized in that, The polyalphaolefin is a non-metallocene polyalphaolefin and / or a metallocene polyalphaolefin. And / or, the polyisobutylene is polyisobutylene with a number average molecular weight of 800 to 2000; And / or, the filler is selected from one or more combinations of talc powder, mica powder, kaolin, slag powder, wood flour, calcium carbonate, magnesium carbonate and barium sulfate; And / or, the thickener is selected from at least one of silica, organobentonite, starch resin, tannin, and grafted starch; And / or, the reinforcing fiber is selected from at least one of natural fibers, synthetic fibers and mineral fibers.

4. The high-performance, flame-retardant water-based shield tail sealant according to claim 1, characterized in that, The polyalphaolefin is a metallocene polyalphaolefin with a kinematic viscosity at 100°C ≥2000 cst. And / or, the polyisobutylene is polyisobutylene with a number average molecular weight of 1000 to 1800; And / or, the mass ratio of sodium poly(isobutylene-alt-succinate) to deionized water is 0.15:1 to 0.30:1; And / or, the filler is selected from a combination of calcium carbonate and barium sulfate, wherein the mass fraction of calcium carbonate is 20-25% and the mass fraction of barium sulfate is 2-5%; And / or, the thickener is selected from silica, and the mass fraction of silica is 8-12%; And / or, the reinforcing fiber is a natural fiber selected from one or more of wood fibers, cotton fibers, flax fibers, bamboo fibers, and hemp fibers.

5. The high-performance, flame-retardant water-based shield tail sealant according to claim 1, characterized in that, The polyalphaolefin is selected from at least one of mPAO2000, mPAO5500, mPAO10000 and mPAO20000; And / or, the polyisobutylene is polyisobutylene with a number average molecular weight of 1300; And / or, the reinforcing fiber is selected from cotton fiber, and the mass fraction of the reinforcing fiber is 1.0% to 2.0%.

6. The high-performance, flame-retardant water-based shield tail sealant according to claim 1, characterized in that, The molecular weight of the poly(isobutylene-alt-succinic acid) sodium is 300,000-350,000.

7. A method for preparing a high-performance, flame-retardant water-based shield tail sealant according to any one of claims 1-6, characterized in that, Includes the following steps: 1) Oil phase premixing: Polyalphaolefin and polyisobutylene are added to a premixing vessel and heated to 80-90°C under stirring to obtain a uniformly mixed oil phase; 2) Preparation of aqueous phase and emulsion system: Sodium poly(isobutylene-alt-succinate) is added to deionized water and stirred to dissolve or disperse in the range of room temperature to 60°C to obtain a uniform aqueous emulsion; 3) Emulsification and dispersion: Under the condition of maintaining the oil phase temperature at 80-90℃, the aqueous emulsion obtained in step 2) is slowly added to the oil phase obtained in step 1) under stirring or shearing conditions, so that the deionized water is uniformly dispersed in the oil phase under the action of sodium poly(isobutylene-alt-succinate) to form a stable water-in-oil emulsion. 4) Meshing and mixing: Transfer the water-in-oil emulsion material obtained in step 3) to the meshing machine, adjust the material temperature to 80-90℃, and add filler, thickener and reinforcing fiber in sequence under meshing conditions. After each addition, continue meshing for 20-30 minutes until the material is uniform, and the high-performance, flame-retardant water-based shield tail sealant as described in any one of claims 1 to 6 is obtained.

8. The preparation method according to claim 7, characterized in that: Step 2) The mass fraction of sodium poly(isobutylene-alt-succinate) in deionized water is 10% to 25%, and the mixture is stirred for 10 to 60 minutes at a shear speed of ≥500 rpm to ensure complete dissolution or dispersion. And / or, in step 3), the time for adding the aqueous emulsion to the oil phase is controlled within 10 to 60 minutes, and a mechanical stirring or high shear dispersion device with a rotation speed of 500 to 2000 rpm is used to form a stable water-in-oil structure. And / or, in step 4), the total engagement time is 60 to 120 minutes, and the material temperature is controlled at 70 to 90°C at the end of engagement, so as to obtain a paste-like sealing grease with a zero-thrust depth of 220 to 250.

9. A method for sealing the tail of a tunnel boring machine, characterized in that, Using the high-performance, flame-retardant water-based shield tail sealant according to any one of claims 1 to 6, the sealant is continuously injected between the wire brushes of the shield tail by the shield machine grease injection pump, so that the sealant fills the interior of the wire brushes and the gaps between the wire brushes to form a sealing layer. The pumping rate of the sealant under the conditions of 1 MPa and 25°C is not less than 40 g / min, and it remains water-proof under a water pressure of 3.5 MPa.

10. The shield tail sealing method for a tunnel boring machine according to claim 9, characterized in that, The tunnel boring machine is used for long-distance, deep-buried, or high-water-pressure tunnel construction. The sealing layer passes the water erosion resistance test and seawater erosion test at 38°C, and the ignition point of the sealing grease is not lower than 295°C in the construction environment.

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