A polyether polyurethane composition for track fastenings and a process for its preparation

Abstract

The present application belongs to the field of advanced polymer materials for rail transit, and discloses a polyether polyurethane composition for rail fasteners and a preparation method thereof. The components of the polyether polyurethane composition by weight parts include: 60-70 parts of thermoplastic polyurethane elastomer, 10-15 parts of hydrogenated styrene-butadiene-styrene block copolymer, 8-10 parts of thermoplastic polyester elastomer, 3-5 parts of whisker, 3-5 parts of glass microbead, 2-3 parts of carbon black, 0.2-0.5 parts of coupling agent, 0-10 parts of composite flame retardant, 0.5-1 parts of release agent, 0.1-0.3 parts of antioxidant, and 0.1-0.3 parts of light stabilizer. The whisker and glass microbead are coated and dispersed in the thermoplastic polyurethane elastomer, which has sufficient rigidity support under static load and exhibits low dynamic rigidity under high-frequency impact, thereby realizing good buffering performance. The material use life is prolonged by avoiding thermal fatigue failure under high-frequency dynamic load.

Description

Technical Field

[0001] This invention relates to the field of advanced polymer materials technology for rail transit, specifically to a polyether-type polyurethane composition for rail fasteners and its preparation method. Background Technology

[0002] The elastic pads of track fasteners are important vibration damping components placed between the rails and sleepers. When high-frequency vibrations occur, the elastic pads effectively absorb and disperse the vibration energy through their own elastic deformation, quickly converting the destructive mechanical energy into heat energy generated by the friction of the elastomer molecular chains and dissipating it. This reduces the impact on the track structure, lowers vibration and noise, and ensures the smoothness and comfort of train operation.

[0003] Most existing railway track fasteners use rubber pads for their elastic plates. However, the addition of large amounts of carbon black and calcium powder results in a high permanent deformation rate in the rubber material. Under high-frequency impact, creep leads to performance degradation, making it prone to thermal aging. This causes rapid decline in cushioning and vibration damping performance, shortening service life and increasing maintenance costs while also affecting the stability of the fasteners.

[0004] A series of modifications and improvements have been made to address the problems of easy aging and cracking, and insufficient elasticity of track rubber pads. For example, CN114656698B discloses a track rubber pad material and its preparation method. By adding an organic polymer end-capped with 2,2'-methylenebis(4-methyl-6-tert-butylphenol) to nitrile rubber, a rubber pad with excellent damping performance is prepared, while also meeting the physical and mechanical properties of track pads, significantly improving the ability to mitigate track vibration and reduce noise. CN116462894B discloses a high-performance track rubber pad material, its preparation method, and its structure. By adding thermoplastic polyester elastomers and polycarbonate to rubber, the hardness, tensile strength, static stiffness, and other mechanical properties of the pad are improved.

[0005] Due to the high requirements for durability, creep resistance, and high-frequency vibration resistance of elastic pads in high-speed railways, traditional rubber elastic pads are no longer suitable for the frequent impacts of high-speed trains. Currently, polyurethane is gradually being used as the elastic pad material in high-speed rail fasteners. Compared to traditional rubber, polyurethane has better compressibility, deformability, and dynamic fatigue resistance, making it suitable for frequent deformation damping. It maintains good resilience even under long-term high-load deformation, making it more suitable for the high-frequency vibrations of high-speed rail tracks.

[0006] When subjected to the high-frequency vibrations of high-speed trains, polyurethane elastic pads require high hardness to achieve dynamic load, leading to increased dynamic stiffness. High dynamic stiffness not only affects damping performance but also causes material cracking or failure under repeated loading. To overcome this problem, existing technologies use polyurethane foaming to reduce the dynamic-to-static stiffness ratio. For example, CN117024947B discloses a polyurethane elastic pad and its continuous preparation method; CN101942786B discloses a rail pad and its preparation method. Both use on-site reaction, foaming, and curing to prepare microporous polyurethane elastic pads. On the one hand, the on-site foaming process is complex and difficult to control; on the other hand, on-site raw material storage requirements are high, affecting large-scale production. Furthermore, foaming of polyurethane materials has a significant impact on mechanical strength. Summary of the Invention

[0007] To address the current issues of high dynamic stiffness in polyurethane used for track fastener elastic pads, which affects damping performance and leads to fatigue failure under repeated loading, this invention proposes a polyether-type polyurethane composition for track fasteners. By introducing SEBS-modified whiskers and glass microspheres into the polyether-type thermoplastic polyurethane, not only is the dynamic stiffness reduced and high-frequency damping increased, but impact energy is also effectively dissipated, internal heat accumulation is alleviated, and fatigue aging is prevented.

[0008] To achieve the above-mentioned technical objectives, the present invention adopts the following technical means: In a first aspect, this application provides a polyether-type polyurethane composition for track fasteners, wherein, by weight, the polyether-type polyurethane composition comprises the following components: 60-70 parts of thermoplastic polyurethane elastomer, 10-15 parts of hydrogenated styrene-butadiene-styrene block copolymer, 8-10 parts of thermoplastic polyester elastomer, 3-5 parts of whiskers, 3-5 parts of glass microspheres, 2-3 parts of carbon black, 0.2-0.5 parts of coupling agent, 0-10 parts of composite flame retardant, 0.5-1 part of release agent, 0.1-0.3 parts of antioxidant, and 0.1-0.3 parts of light stabilizer; The thermoplastic polyurethane elastomer is a polyether-type thermoplastic polyurethane elastomer with a Shore A hardness of 70A-85A. The thermoplastic polyester elastomer is a thermoplastic polyester elastomer with polyether as the soft segment; The Shore A hardness of the hydrogenated styrene-butadiene-styrene block copolymer is 40A-60A; The whiskers are 50-100 μm in length; The glass microspheres are spherical glass microspheres with a particle size of 20-100 μm.

[0009] Preferably, the soft segments of the polyether-type thermoplastic polyurethane elastomer include, but are not limited to, any one of polypropylene glycol, polyethylene glycol, and polytetrahydrofuran ether glycol. Polyether-type thermoplastic polyurethane elastomers, using polyether polyols as soft segments, exhibit good dynamic flexibility and hydrolysis resistance. Polyether-type thermoplastic polyurethane elastomers with a Shore A hardness of 70A-85A combine elasticity and support, exhibiting a high resilience. This meets the basic requirements for hardness and static stiffness of elastic pads in high-speed rail track fasteners, facilitating the adjustment of static stiffness to a range of 20-60 kN / mm.

[0010] Hydrogenated styrene-butadiene-styrene block copolymer (SEBS) has high elasticity and toughness, and a certain degree of compressibility. SEBS can effectively encapsulate inorganic materials such as whiskers and glass microspheres to form a strong interface, which not only promotes the dispersion of inorganic materials, but also forms a soft-hard gradient damping material with soft encapsulation of hard materials.

[0011] Thermoplastic polyester elastomers (TPEEs) combine the elasticity of rubber with the properties of engineering plastics. TPEEs with polyether as the soft segment exhibit good strength, hardness, heat resistance, and elasticity, which can improve the strength and heat resistance of compositions, broaden the damping temperature range, and provide good compatibility with polyether-based polyurethane elastomers. Due to their hard segment crystalline structure, TPEEs with polyether as the soft segment can provide a more stable dynamic response, exhibiting high resilience and low hysteresis, and can reduce the dynamic-to-static stiffness ratio of compositions.

[0012] Preferably, the whiskers are at least one of calcium sulfate whiskers, calcium carbonate whiskers, calcium silicate whiskers, silicon carbide whiskers, and magnesium hydroxide whiskers. The whiskers are micron-sized needles; their addition significantly improves the material's load-bearing capacity and toughness, effectively prevents crack propagation through stress transfer, and enhances the material's fatigue resistance. Preferably, the glass microspheres are large-diameter spherical glass microspheres with a particle size of 50-100 μm. Large-diameter spherical glass microspheres are easy to disperse, improving stress dispersion under dynamic loads. When subjected to alternating loads in an elastic matrix, microscopic slippage occurs between the large-diameter particles and the matrix, reducing the dynamic-to-static stiffness ratio and increasing the damping properties of the elastic pad.

[0013] Preferably, the carbon black particle size is 100-500 nm. Using carbon black with a larger particle size facilitates dispersion, reduces localized stress concentration, lowers intramolecular chain friction, alleviates energy accumulation, conducts internal heat to the outside, and delays thermal aging. Preferably, the coupling agent is at least one of a silane coupling agent, a titanate coupling agent, or an aluminate coupling agent.

[0014] Preferably, the composite flame retardant is a composite flame retardant made by compounding a phosphate ester flame retardant and zinc borate in a mass ratio of 8:1. Phosphate ester flame retardants have certain plasticizing properties, and large-scale use will not significantly affect the basic hardness of the material. More preferably, the phosphate ester flame retardant is selected from either resorcinol bis(diphenyl phosphate) (RDP) or bisphenol A-bis(diphenyl phosphate) (BDP). In a specific embodiment, when flame retardant performance is required, a composite flame retardant is composed of bisphenol A-bis(diphenyl phosphate) and zinc borate in a mass ratio of 8:1. The synergistic effect of phosphorus flame retardancy and the formation of a glassy molten layer by zinc borate achieves a UL 94 flame retardant rating of V-0 (3.2 mm).

[0015] Preferably, the mold release agent is either zinc stearate or erucamide. Thermoplastic polyurethane elastomers readily adhere to metals, causing mold adhesion and making demolding difficult during compression molding or injection molding of elastic pads. Adding a mold release agent allows for rapid demolding, improving production efficiency.

[0016] Preferably, the antioxidant is a hindered phenolic antioxidant, such as at least one of 2,6-di-tert-butyl-p-cresol (antioxidant 246), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076).

[0017] Preferably, the light stabilizer is selected from ultraviolet absorbers and / or hindered amine light stabilizers.

[0018] Further, the ultraviolet absorber is at least one of benzophenone, benzotriazole, or triazine ultraviolet absorbers. The benzophenone ultraviolet absorber is selected from UV-9, UV-24, and UV-531; the benzotriazole ultraviolet absorber is selected from UV-326 and UV-234; and the triazine ultraviolet absorber is selected from UV-1164 and UV-1577.

[0019] Furthermore, the hindered amine light stabilizer is selected from either light stabilizer 944 or light stabilizer 622.

[0020] Furthermore, this application provides a method for preparing a polyether-type polyurethane composition for rail fasteners, the method comprising the following steps: S1. Add whiskers, glass microspheres, carbon black, and coupling agent to a high-speed mixer for high-speed stirring and modification. Then add hydrogenated styrene-butadiene-styrene block copolymer and thermoplastic polyester elastomer and mix evenly. Then convey to a twin-screw extruder for melt extrusion granulation to obtain a soft-hard gradient damping material. S2. The thermoplastic polyurethane elastomer, soft-hard gradient damping material, composite flame retardant, mold release agent, antioxidant, and light stabilizer are mixed evenly in a high-speed mixer, melt-extruded through a twin-screw extruder, and pelletized through a water ring die to obtain a polyether-type polyurethane composition for track fasteners.

[0021] Preferably, the twin-screw extruder is a parallel co-rotating twin-screw extruder with a screw length-to-diameter ratio (L / D) > 40, which extends the residence time of the material within the screw and achieves better shear dispersion modification. The temperature of the melt section of the screw is controlled at 190-220℃, and the screw speed is 200-300 rpm. When the screw length-to-diameter ratio is small, using a high speed can compensate for insufficient shear dispersion.

[0022] The principle and beneficial effects of this invention are as follows: 1. Simply adding toughening agents or microfoaming to thermoplastic polyester elastomers can reduce dynamic stiffness, but the static stiffness of the material will also be significantly reduced, failing to form effective support. This invention modifies the surface of whiskers and glass microspheres through surface coupling, then melt-extrudes them with thermoplastic polyester elastomers and hydrogenated styrene-butadiene-styrene block copolymers to obtain a soft-hard gradient damping material. The damping material is dispersed in the thermoplastic polyurethane elastomer to form uniformly dispersed damping elastic particles. This rigid particle-elastomer composite maintains good static support (stable static stiffness). When subjected to high-frequency impact, SEBS exhibits high elasticity and toughness, reducing the material's dynamic stiffness (i.e., dynamic modulus) and demonstrating high damping characteristics. Whiskers have reinforcing and toughening effects; when the elastic pad is impacted by a load, the micron-sized whiskers are pulled out, effectively dissipating impact energy, alleviating internal heat accumulation, and preventing fatigue aging. Spherical glass microspheres can effectively disperse stress, improve energy dissipation under dynamic loads, maintain support, reduce the dynamic-to-static stiffness ratio, and increase the damping properties of the elastic pad.

[0023] 2. This invention utilizes a soft-to-hard gradient damping material dispersed within a thermoplastic polyester elastomer of suitable hardness to ensure sufficient hardness and stiffness support under static loads. Under dynamic impacts, it exhibits low dynamic stiffness, thus achieving good cushioning. This avoids thermal fatigue failure under high-frequency dynamic loads and extends the material's service life.

[0024] 3. The polyether-type polyurethane composition for track fasteners obtained by the present invention can be directly used for rapid prototyping processes such as molding and injection molding, eliminating the need for complicated foaming process control procedures and greatly improving production efficiency. Detailed Implementation

[0025] The present application will be further described in detail below with reference to the embodiments. In particular, it should be noted that: unless otherwise specified, the following embodiments can be implemented according to the conventional conditions understood in the art; unless otherwise stated, the terminology used is as commonly understood by those skilled in the art; the materials used in the preparation can all be obtained commercially, and except for special raw material limitations, the other raw materials are all general raw materials.

[0026] Technical parameters of some raw materials and equipment used in the implementation plan: Polyether-type polyurethane: Grade HF-4080A, Shore A hardness 80A, tensile strength 25MPa, elongation 550%, Zhejiang Huafeng Thermoplastic Polyurethane Co., Ltd.

[0027] Thermoplastic polyester elastomer: Grade Hytrel@ HTR8163HVBK, Shore D hardness 65D, tensile strength 44MPa, elongation 300%, DuPont.

[0028] Hydrogenated styrene-butadiene-styrene block copolymer: Grade YH-688, Shore A hardness 45A, tensile strength 10MPa, Sinopec Hunan Petrochemical Co., Ltd.

[0029] Parallel co-rotating twin-screw extruder: diameter Φ65mm, L / D=44.

[0030] Example 1 S1. Add 3 kg of calcium sulfate whiskers (diameter 2-5 μm, D50 length 80-100 μm), 4 kg of spherical glass microspheres (D90 particle size 50-100 μm), 3 kg of carbon black (rubber-specific carbon black with a particle size of 100-500 nm), and 0.3 kg of coupling agent KH-550 to a high-speed mixer and stir at 80℃ and 700 rpm for 30 min for surface modification. Then add 12 kg of hydrogenated styrene-butadiene-styrene block copolymer (YH-688) and thermoplastic polyester elastomer (Hytrel@ 10 kg of HTR8163HVBK was mixed evenly and fed into a Φ65 parallel co-rotating twin-screw extruder for melt extrusion modification. The extrusion temperature control for each zone was as follows: Zone 1 160℃, Zone 2 180℃, Zone 3 200℃, Zone 4 210℃, Zone 5 210℃, Zone 6 210℃, Zone 7 200℃, Zone 8 190℃, Zone 9 170℃, and Zone 10 160℃; the screw speed was 300 rpm; a soft-hard gradient damping material was obtained. S2. The soft-hard gradient damping material obtained in step S1 is mixed evenly with 65 kg of polyether-type thermoplastic polyurethane elastomer (HF-4080A), 0.5 kg of release agent erucamide, 0.3 kg of antioxidant 1010, and 0.2 kg of hindered amine light stabilizer 944 in a high-speed mixer. The mixture is then extruded through a Φ65 parallel co-rotating twin-screw extruder with the following temperature control for each zone: Zone 1 140℃, Zone 2 160℃, Zone 3 190℃, Zone 4 200℃, Zone 5 200℃, Zone 6 210℃, Zone 7 200℃, Zone 8 180℃, Zone 9 170℃, and Zone 10 150℃; the screw speed is 250 rpm. The mixture is then pelletized through a water ring die to obtain a polyether-type polyurethane composition for track fasteners.

[0031] Example 2 S1. Add 4 kg of calcium carbonate whiskers (5-6 μm in diameter, 50-100 μm in D50 length), 4 kg of spherical glass microspheres (50-100 μm in D90 particle size), 2 kg of carbon black (rubber-specific carbon black with a particle size of 100-500 nm), and 0.4 kg of coupling agent KH-550 to a high-speed mixer and stir for 30 min at 80℃ and 700 rpm for surface modification. Then add 15 kg of hydrogenated styrene-butadiene-styrene block copolymer (YH-688) and thermoplastic polyester elastomer (Hytrel@ 8 kg of HTR8163HVBK was mixed evenly and fed into a Φ65 parallel co-rotating twin-screw extruder for melt extrusion. The extrusion temperature control for each zone was as follows: Zone 1 160℃, Zone 2 180℃, Zone 3 200℃, Zone 4 210℃, Zone 5 210℃, Zone 6 210℃, Zone 7 200℃, Zone 8 190℃, Zone 9 170℃, and Zone 10 160℃; the screw speed was 300 rpm; after extrusion granulation, a soft-hard gradient damping material was obtained. S2. The soft-hard gradient damping material obtained in step S1 is mixed evenly with 70 kg of polyether-type thermoplastic polyurethane elastomer (HF-4080A), 9 kg of composite flame retardant, 0.8 kg of zinc stearate release agent, 0.3 kg of antioxidant 1010, and 0.2 kg of hindered amine light stabilizer 944 in a high-speed mixer. The mixture is then extruded through a Φ65 parallel co-rotating twin-screw extruder with the following temperature control for each zone: Zone 1 140℃, Zone 2 160℃, Zone 3 190℃, Zone 4 200℃, Zone 5 200℃, Zone 6 210℃, Zone 7 200℃, Zone 8 180℃, Zone 9 170℃, and Zone 10 150℃; the screw speed is 200 rpm. The mixture is then pelletized through a water ring die to obtain a polyether-type polyurethane composition for track fasteners. The composite flame retardant is a mixture of bisphenol A-bis(diphenyl phosphate) and zinc borate at a mass ratio of 8:1.

[0032] For elastic pads with flame retardant requirements, composite flame retardants can work synergistically to achieve a UL 94 flame retardant rating of V-0 (thickness 3.2mm) without significantly affecting the hardness of the elastic pad.

[0033] Example 3 S1. Add 3 kg of calcium sulfate whiskers (diameter 2-5 μm, D50 length 80-100 μm), 5 kg of spherical glass microspheres (D90 particle size 50-100 μm), 2 kg of carbon black (rubber-specific carbon black with a particle size of 100-500 nm), and 0.5 kg of coupling agent KH-550 to a high-speed mixer and stir at 80℃ and 700 rpm for 30 min for surface modification. Then add 10 kg of hydrogenated styrene-butadiene-styrene block copolymer (YH-688) and thermoplastic polyester elastomer (Hytrel@ 10 kg of HTR8163HVBK was mixed evenly and fed into a Φ65 parallel co-rotating twin-screw extruder for melt extrusion. The extrusion temperature control for each zone was as follows: Zone 1 160℃, Zone 2 180℃, Zone 3 200℃, Zone 4 210℃, Zone 5 210℃, Zone 6 210℃, Zone 7 200℃, Zone 8 190℃, Zone 9 170℃, and Zone 10 160℃; the screw speed was 300 rpm; after extrusion granulation, a soft-hard gradient damping material was obtained. S2. The soft-hard gradient damping material obtained in step S1 is mixed evenly with 60 kg of polyether-type thermoplastic polyurethane elastomer (HF-4080A), 0.5 kg of release agent erucamide, 0.3 kg of antioxidant 1076, and 0.3 kg of UV-326 in a high-speed mixer. The mixture is then extruded through a Φ65 parallel co-rotating twin-screw extruder with the following temperature control for each zone: Zone 1 140℃, Zone 2 160℃, Zone 3 190℃, Zone 4 200℃, Zone 5 200℃, Zone 6 210℃, Zone 7 200℃, Zone 8 180℃, Zone 9 170℃, and Zone 10 150℃. The screw speed is 300 rpm. The mixture is then pelletized through a water ring die to obtain a polyether-type polyurethane composition for use in track fasteners.

[0034] Comparative Example 1 97 kg of polyether-type thermoplastic polyurethane elastomer (HF-4080A), 0.5 kg of release agent erucamide, 0.3 kg of antioxidant 1010, and 0.2 kg of hindered amine light stabilizer 944 were mixed evenly in a high-speed mixer. The mixture was then extruded through a Φ65 parallel co-rotating twin-screw extruder with the following temperature control for each zone: Zone 1 140℃, Zone 2 160℃, Zone 3 190℃, Zone 4 200℃, Zone 5 200℃, Zone 6 210℃, Zone 7 200℃, Zone 8 180℃, Zone 9 170℃, and Zone 10 150℃. The screw speed was 200 rpm. The mixture was then pelletized through a water ring die to obtain a polyether-type polyurethane composition for use in rail fasteners.

[0035] This comparative example uses the original formula before improvement, without the addition of soft-hard gradient damping material. The material has slightly lower static stiffness, but its dynamic modulus increases under load impact, resulting in relatively high static and dynamic stiffness. This intensifies the impact on the track, reduces vibration damping performance, and affects resilience and fatigue durability.

[0036] Comparative Example 2 The following materials were added: 3 kg of calcium sulfate whiskers (diameter 2-5 μm, D50 length 80-100 μm), 4 kg of spherical glass microspheres (D90 particle size 50-100 μm), 3 kg of carbon black (rubber-specific carbon black with a particle size of 100-500 nm), 0.3 kg of coupling agent KH-550, 12 kg of hydrogenated styrene-butadiene-styrene block copolymer (YH-688), and thermoplastic polyester elastomer (Hytrel@). 10 kg of HTR8163HVBK, 65 kg of polyether-type thermoplastic polyurethane elastomer (HF-4080A), 0.5 kg of release agent erucamide, 0.3 kg of antioxidant 1010, and 0.2 kg of hindered amine light stabilizer 944 were mixed evenly in a high-speed mixer. The mixture was then extruded through a Φ65 parallel co-rotating twin-screw extruder with the following temperature control for each zone: Zone 1 140℃, Zone 2 160℃, Zone 3 190℃, Zone 4 200℃, Zone 5 200℃, Zone 6 210℃, Zone 7 200℃, Zone 8 180℃, Zone 9 170℃, and Zone 10 150℃; the screw speed was 200 rpm. The mixture was then pelletized through a water ring die to obtain a polyether-type polyurethane composition for use in rail fasteners.

[0037] In this comparative example, SEBS, whiskers, spherical glass microspheres, etc., were not pre-coupled and extruded to form a soft-hard damping material, but were directly added to the extrusion granulation process. This increased the hardness and static stiffness of the material, and the dynamic modulus under load impact, resulting in a relatively large dynamic and static stiffness.

[0038] Comparative Example 3 This comparative example is basically the same as Example 1, except that calcium sulfate whiskers were removed and replaced with spherical glass microspheres. The fatigue resistance of the resulting material was reduced.

[0039] Comparative Example 4 This comparative example is basically the same as Example 1, except that the large-diameter spherical glass microspheres are replaced with fine spherical glass microspheres with a particle size of less than 20 μm. Under load impact, the micro-interface detachment between the fine-diameter particles and the matrix is ​​less pronounced, which is not conducive to reducing dynamic stiffness.

[0040] Performance evaluation: The polyether-type polyurethane compositions of the examples and comparative examples were used for molding elastic pads of WJ-7 type fasteners (suitable for ballastless track high-speed railways with speeds of 250–350 km / h).

[0041] Elastic pad molding parameters: mold temperature 200℃, molding pressure 75MPa, holding time 2min.

[0042] The Shore A hardness, static stiffness, dynamic-to-static stiffness ratio, and fatigue resistance of the elastic pad under 3 million load cycles were tested.

[0043] (a) Shore hardness test The Shore A hardness of the elastic pad was tested according to standard GB / T 531.1-2008 "Test method for indentation hardness of vulcanized rubber or thermoplastic rubber - Part 1: Shore hardness tester method (Shore hardness)". The test results are shown in Table 1.

[0044] (ii) Static stiffness test The tests were conducted according to Appendix A of standard TB / T 3395.1-2015 "High-speed railway fasteners - Part 1: General technical conditions". The design static stiffness standard is 30-40 kN / mm to meet the technical requirements of high-speed railway track fasteners. The test results are shown in Table 1.

[0045] (III) Dynamic-to-static stiffness ratio (Kd / Ks) test Tests were conducted according to Appendix B of TB / T 3395.1-2015 "High-Speed ​​Railway Fasteners Part 1: General Technical Conditions". The optimal dynamic-to-static stiffness ratio (Kd / Ks) was designed to be ≤1.3. The dynamic-to-static stiffness ratio comprehensively reflects the vibration reduction, rebound, damping, and fatigue resistance performance of the elastic pad. The lower the dynamic-to-static stiffness ratio, the better the rebound performance of the elastic pad under dynamic impact, and the better the vibration transmission effect, which is beneficial to improving the vibration reduction effect of rail transit and has better damping performance. The test results are shown in Table 1.

[0046] Table 1: Hardness, Static Stiffness, and Dynamic-Static Stiffness Ratio of Elastic Pads (iv) Fatigue resistance test Tests were conducted according to Appendix C of TB / T 3395.1-2015 "High-Speed ​​Railway Fasteners Part 1: General Technical Conditions". An 80kN load was applied to the elastic pad at a frequency of 4Hz. After 3 million load cycles, the fatigue resistance was determined by measuring the permanent deformation and static stiffness changes of the elastic pad. Elastic pads used in high-speed railway track fasteners are required to show no stress cracking after 3 million load cycles, with permanent deformation not exceeding 10% and static stiffness change rate not exceeding 15%. Furthermore, an additional 1 million cycles were performed after the initial 3 million load cycles to assess fatigue damage. The test results are shown in Table 2.

[0047] Table 2: Fatigue Resistance of Elastic Pads From the Shore A hardness, static stiffness, dynamic-to-static stiffness ratio, and fatigue resistance data of the elastic pads tested above, it can be concluded that: This invention coats the surface of whiskers and glass microspheres with an elastic material to form a soft-to-hard gradient damping material, creating uniformly dispersed damping elastic particles within a thermoplastic polyurethane elastomer. These damping particles, combining rigid particles and an elastomer, can effectively maintain stable static support; under load impact, they exhibit a low dynamic-to-static stiffness ratio and high damping characteristics; they not only adapt to the high-frequency impacts of high-speed rail but also effectively dissipate impact energy, alleviate internal heat accumulation, and prevent fatigue aging. This invention yields a polyether-type polyurethane composition that can be directly used in the rapid prototyping of rail fasteners, such as molding and injection molding, without the need for foaming, simplifying subsequent application processes and making it suitable for mass production of elastic pads for rail fasteners. In addition, the elastic pad prepared by the polyether polyurethane composition of the present invention was tested by hot air aging (70℃×168h). The tensile strength before aging was >23MPa and the tensile strength after aging was >20MPa. The heat resistance was stable and fully met the technical requirements specified in T / ZZB 1443-2019.

Claims

1. A polyether-type polyurethane composition for track fasteners, characterized in that, By weight, the polyether-type polyurethane composition comprises the following components: 60-70 parts of thermoplastic polyurethane elastomer, 10-15 parts of hydrogenated styrene-butadiene-styrene block copolymer, 8-10 parts of thermoplastic polyester elastomer, 3-5 parts of whiskers, 3-5 parts of glass microspheres, 2-3 parts of carbon black, 0.2-0.5 parts of coupling agent, 0-10 parts of composite flame retardant, 0.5-1 part of release agent, 0.1-0.3 parts of antioxidant, and 0.1-0.3 parts of light stabilizer; The thermoplastic polyurethane elastomer is a polyether-type thermoplastic polyurethane elastomer with a Shore A hardness of 70A-85A. The thermoplastic polyester elastomer is a thermoplastic polyester elastomer with polyether as the soft segment; The Shore A hardness of the hydrogenated styrene-butadiene-styrene block copolymer is 40A-60A; The whiskers are 50-100 μm in length; The glass microspheres are spherical glass microspheres with a particle size of 20-100 μm; The polyether-type polyurethane composition for track fasteners is prepared by the following method: S1. Add whiskers, glass microspheres, carbon black, and coupling agent to a high-speed mixer for high-speed stirring and modification. Then add hydrogenated styrene-butadiene-styrene block copolymer and thermoplastic polyester elastomer and mix evenly. Then convey to a twin-screw extruder for melt extrusion granulation to obtain a soft-hard gradient damping material. S2. The thermoplastic polyurethane elastomer, soft-hard gradient damping material, composite flame retardant, mold release agent, antioxidant, and light stabilizer are mixed evenly in a high-speed mixer, melt-extruded through a twin-screw extruder, and pelletized through a water ring die to obtain a polyether-type polyurethane composition for track fasteners.

2. The polyether-type polyurethane composition for track fasteners according to claim 1, characterized in that, The soft segment of the polyether-type thermoplastic polyurethane elastomer is any one of polypropylene glycol, polyethylene glycol, or polytetrahydrofuran ether glycol.

3. The polyether-type polyurethane composition for track fasteners according to claim 1, characterized in that, The whiskers are at least one of calcium sulfate whiskers, calcium carbonate whiskers, calcium silicate whiskers, silicon carbide whiskers, and magnesium hydroxide whiskers.

4. The polyether-type polyurethane composition for track fasteners according to claim 1, characterized in that, The glass microspheres are large-diameter spherical glass microspheres with a particle size of 50-100μm.

5. The polyether-type polyurethane composition for track fasteners according to claim 1, characterized in that, The carbon black has a particle size of 100-500 nm.

6. The polyether-type polyurethane composition for track fasteners according to claim 1, characterized in that, The coupling agent is at least one of a silane coupling agent, a titanate coupling agent, or an aluminate coupling agent.

7. The polyether-type polyurethane composition for track fasteners according to claim 1, characterized in that, The composite flame retardant is a mixture of phosphate ester flame retardant and zinc borate in a mass ratio of 8:

1.

8. The polyether-type polyurethane composition for track fasteners according to claim 1, characterized in that, The release agent is either zinc stearate or erucamide.

9. A method for preparing a polyether-type polyurethane composition for track fasteners according to any one of claims 1-8, the method comprising the following steps: S1. Add whiskers, glass microspheres, carbon black, and coupling agent to a high-speed mixer for high-speed stirring and modification. Then add hydrogenated styrene-butadiene-styrene block copolymer and thermoplastic polyester elastomer and mix evenly. Then convey to a twin-screw extruder for melt extrusion granulation to obtain a soft-hard gradient damping material. S2. The thermoplastic polyurethane elastomer, soft-hard gradient damping material, composite flame retardant, mold release agent, antioxidant, and light stabilizer are mixed evenly in a high-speed mixer, melt-extruded through a twin-screw extruder, and pelletized through a water ring die to obtain a polyether-type polyurethane composition for track fasteners.

10. The method for preparing the polyether-type polyurethane composition for track fasteners according to claim 9, characterized in that, The twin-screw extruder is a parallel co-rotating twin-screw extruder with a screw length-to-diameter ratio (L / D) > 40; the screw speed of the twin-screw extruder is 200-300 rpm.

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