Railway locomotive double-oil-resistant silane crosslinking flame-retardant polyolefin sheath material and preparation method thereof

Abstract

The invention relates to the technical field of cable sheath materials, and discloses a railway locomotive double-oil-resistant silane crosslinking flame-retardant polyolefin sheath material which is prepared from the following raw materials in parts by weight: a material A: 1-2 parts of a silane coupling agent A-172; 0.5 to 1 part of a silane coupling agent A-171; 0.1 to 0.2 part of an initiator; and 100 parts of master batch. The invention also discloses a preparation method of the double-oil-resistant silane crosslinking flame-retardant polyolefin sheath material for the railway locomotive, which comprises the following steps: S1, preparing the material A and the material B according to a formula: preparing the components of the material A and the components of the material B according to a preset ratio, and uniformly mixing the required raw materials. By adopting the combination of the high-crystallinity mLLDPE resin and the high-VA-content EVA rubber, a composite halogen-free flame retardant system, a silane crosslinking technology and a microwave-assisted extrusion process, the oil resistance, flame retardance, mechanical strength and production efficiency of the cable sheath are remarkably improved, and meanwhile, the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of cable sheath materials, and specifically to a double oil-resistant silane cross-linked flame-retardant polyolefin sheath material for railway locomotives and a preparation method thereof. Background Art

[0002] The cable sheath materials used in the railway transportation industry are mainly composed of polyolefin materials and halogen-containing polymer materials. Although halogen-containing materials have good electrical insulation performance and weather resistance, they will release a large amount of toxic gases and black smoke during combustion, which not only seriously threatens the safety of personnel, but also exacerbates the problem of environmental pollution. With the gradual strictness of environmental protection regulations, low-smoke and halogen-free flame-retardant materials have gradually become the trend of the industry's development. In order to adapt to this trend, in recent years, low-smoke and halogen-free silane cross-linked polyolefin materials have been widely used in railway locomotive cables due to their excellent environmental protection performance and flame-retardant characteristics.

[0003] Although the existing silane cross-linked low-smoke and halogen-free flame-retardant polyolefin sheath materials show good environmental protection and flame retardancy in case of fire, reducing the release of toxic gases and black smoke, they still face some challenges in high-temperature and high-pressure oil environments. Traditional halogen-free flame-retardant sheath materials cannot meet the three requirements of oil resistance, mechanical strength, and low-smoke and halogen-free at the same time. Especially in high-temperature and high-pressure oil environments, the existing materials are prone to expansion, deformation, and even damage, which not only affects the service life of the cable, but also may threaten the safety of the cable system. Even at low temperatures, the mechanical properties of some materials cannot effectively ensure the long-term stable operation of the cable system. Therefore, how to improve the oil resistance, mechanical strength, and low-temperature resistance of materials in harsh environments while meeting environmental protection requirements has become an urgent problem to be solved.

[0004] Most of the existing technical solutions focus on optimizing a single performance, such as improving the flame retardancy or environmental protection of the material, but few technologies can improve the oil resistance and mechanical strength of the material while ensuring the halogen-free flame-retardant effect. In addition, traditional production processes, such as high-temperature heat treatment, often result in high energy consumption, high cost, and long reaction time during the production process, and cannot achieve efficient production. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention provides a double oil-resistant silane cross-linked flame-retardant polyolefin sheath material for railway locomotives and a preparation method thereof, which solves the problems of poor oil resistance, insufficient mechanical strength, and difficulty in balancing low-smoke and halogen-free flame-retardant performance of traditional halogen-free flame-retardant sheath materials in high-temperature and high-pressure oil environments.

[0006] To achieve the above objectives, the present invention is realized through the following technical solutions: The double oil-resistant silane cross-linked flame-retardant polyolefin sheath material for railway locomotives is composed of the following raw materials in parts by weight: Material A: Silane coupling agent A-172: 1-2 parts; Silane coupling agent A-171: 0.5-1 part; Initiator: 0.1-0.2 part; Masterbatch: 100 parts; Material B: Color masterbatch: 15-20 parts; mLLDPE4518PA: 15-20 parts; Compatibilizer MC216A: 2-5 parts; MDH: 40-60 parts; Silicone lubricant: 0.5-1 part; Antioxidant 405: 5-10 parts; Antioxidant MB: 5-10 parts; Lubricant zinc stearate: 0.5-1 part; Silane coupling agent A-172: 0.5-0.8 part; Catalyst: 0.2-0.6 part.

[0007] Preferably, the mass ratio of Material A to Material B is 90-92:10-8.

[0008] Preferably, the masterbatch is prepared from the following components by weight: POEC5070D: 5-10 parts; EVM700XL: 2-5 parts; mLLDPE3518CB: 20-25 parts; Compatibilizer MC216A: 3-5 parts; ATH aluminum hydroxide: 40-50 parts; MDH magnesium hydroxide: 10-15 parts; Silicone rubber: 2-5 parts; Antioxidant: 0.2-0.4 part; Copper inhibitor: 0.1-0.3 part; Plasticizer: 0.5-1.0 part; Dispersant: 0.2-0.4 part; Silane coupling agent A-172: 0.3-0.6 part.

[0009] Preferably, the EVM rubber can use a VA content of 50-70%.

[0010] Preferably, the compatibilizer is a maleic anhydride grafted polyethylene compatibilizer or a maleic anhydride grafted ethylene vinyl acetate compatibilizer.

[0011] Preferably, both the ATH aluminum hydroxide and MDH magnesium hydroxide are inorganic flame retardants, and the silicone rubber is vinyl silicone rubber with a vinyl content of 1-5%.

[0012] Preferably, the antioxidant is 1010 or 1076, the copper inhibitor is 1024 or MD-5, the plasticizer is DOTP or DOS, the dispersant is EBS or polyethylene wax, and the silane coupling agent is A-172 or A-151.

[0013] Preferably, the POE is optionally either DOW8200 or Mitsui DF840, with a melt index of 2-5 g / 10 min and a Shore hardness A of 70-80, and the mLLDPE is optionally either 3812PA or SP2520, with a melt index of 2-10 g / 10 min and a crystallinity of 60-70%.

[0014] A preparation method for a double oil-resistant silane-crosslinked flame-retardant polyolefin sheath material for railway locomotives, comprising the following steps: S1. Prepare materials A and B according to the formula: Prepare the components of material A and the components of material B according to a predetermined ratio, and uniformly mix the required raw materials; S2. Mixing and reaction: Mix materials A and B through a twin-screw extruder and carry out a reaction, with the temperature controlled at 180-220 °C and the reaction time being 30-60 min; S3. Silane crosslinking process: Use microwave-assisted reactive extrusion technology to carry out a crosslinking reaction at a temperature of 180-220 °C, with the reaction time being 5-15 min, to promote the crosslinking reaction between the silane coupling agent and the resin matrix and form a three-dimensional network structure; S4. Molding and cooling: Mold the reacted mixture and rapidly cool it through a cooling system to ensure the stability of the morphology and physical properties of the final product The present invention provides a double oil-resistant silane-crosslinked flame-retardant polyolefin sheath material for railway locomotives and a preparation method thereof. It has the following beneficial effects: 1. The present invention adopts a technical solution that combines a high-crystallinity mLLDPE resin with an EVA rubber with a high VA content, achieving excellent oil resistance and mechanical strength in the cable sheath. Through this special material ratio, the problem that traditional halogen-free flame-retardant materials are prone to swelling and deformation in high-temperature and high-pressure oil environments is solved. Compared with traditional polyolefin materials in the prior art, the present invention significantly improves the service life of the sheath, enabling the cable to operate stably for a long time in a more demanding working environment.

[0015] 2. The present invention uses a halogen-free flame retardant system of composite aluminum hydroxide and magnesium hydroxide to enhance the low-smoke and halogen-free flame retardant effect of the cable sheath. Compared with the commonly used halogen-based flame retardant materials in the prior art, the present invention not only avoids the release of toxic gases during combustion but also significantly reduces the generation of black smoke, solving the problem that traditional flame retardant sheaths are prone to release toxic gases in case of fire, seriously threatening the safety of personnel, and significantly enhancing the safety of the railway cable system in case of fire.

[0016] 3. Through the application of formulation optimization and modification technologies, the present invention effectively reduces the production cost and improves the production efficiency. By using silane coupling agents and microwave-assisted reactive extrusion technology, the processing performance of the material is improved, and the energy consumption in high-temperature and high-pressure environments is reduced. Compared with traditional technologies, traditional halogen-free flame retardant sheath materials often require a long heat treatment time during production, while the present invention effectively shortens the reaction time and reduces the material waste in production, significantly enhancing the economic benefits.

[0017] 4. The present invention adopts advanced silane cross-linking technology and microwave-assisted extrusion process, enabling the cable sheath material to not only meet the special requirements of railway locomotive cables but also provide new opportunities for the application of cable sheath materials for other rail transit equipment. Compared with traditional technologies, through novel additives and efficient processing methods, the present invention not only solves the balance problem between high oil resistance and flame retardancy but also enables the material to adapt to a wider range of application scenarios, promoting the technological progress and industrial upgrading of the rail transit equipment manufacturing industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic flow chart of the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than 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 efforts shall fall within the protection scope of the present invention.

[0020] Please refer to the attached Figure 1 , the embodiment of the present invention provides a double oil-resistant silane cross-linked flame retardant polyolefin sheath material for railway locomotives, which is composed of the following raw materials in parts by weight: Material A: Silane coupling agent A-172: 1 - 2 parts; Silane coupling agent A-171: 0.5 - 1 part; Initiator: 0.1 - 0.2 part; Masterbatch: 100 parts; Material B: Masterbatch: 15 - 20 parts; mLLDPE4518PA: 15 - 20 parts; Compatibilizer MC216A: 2 - 5 parts; MDH: 40 - 60 parts; Silicone lubricant: 0.5 - 1 part; Antioxidant 405: 5 - 10 parts; Antioxidant MB: 5 - 10 parts; Lubricant zinc stearate: 0.5 - 1 part; Silane coupling agent A - 172: 0.5 - 0.8 part; Catalyst: 0.2 - 0.6 part.

[0021] The mass ratio of material A to material B is 90 - 92:10 - 8.

[0022] The masterbatch is prepared from the following components by weight: POEC5070D: 5 - 10 parts; EVM700XL: 2 - 5 parts; mLLDPE3518CB: 20 - 25 parts; Compatibilizer MC216A: 3 - 5 parts; ATH aluminum hydroxide: 40 - 50 parts; MDH magnesium hydroxide: 10 - 15 parts; Silicone rubber: 2 - 5 parts; Antioxidant: 0.2 - 0.4 part; Copper inhibitor: 0.1 - 0.3 part; Plasticizer: 0.5 - 1.0 part; Dispersant: 0.2 - 0.4 part; Silane coupling agent A - 172: 0.3 - 0.6 part.

[0023] EVM rubber can use a VA content of 50 - 70%.

[0024] The compatibilizer is maleic anhydride grafted polyethylene compatibilizer or maleic anhydride grafted ethylene vinyl acetate compatibilizer.

[0025] ATH aluminum hydroxide and MDH magnesium hydroxide are both inorganic flame retardants, and the silicone rubber is vinyl silicone rubber with a vinyl content of 1 - 5%.

[0026] The antioxidant is 1010 or 1076, the copper inhibitor is 1024 or MD - 5, the plasticizer is DOTP or DOS, the dispersant is EBS or polyethylene wax, and the silane coupling agent is A - 172 or A - 151.

[0027] POE can be either DOW 8200 or Mitsui DF840, with a melt index of 2 - 5 g / 10 min and a Shore hardness A of 70 - 80. mLLDPE can be either 3812PA or SP2520, with a melt index of 2 - 10 g / 10 min and a crystallinity of 60 - 70%.

[0028] Specifically, the formulation of material A includes silane coupling agents A - 172 and A - 171, initiators, and masterbatch. The use of silane coupling agents A - 172 and A - 171 enables a stronger interfacial adhesion force to be formed between the inorganic fillers (such as aluminum hydroxide and magnesium hydroxide) and the resin matrix. These coupling agents contain silane groups, which can react with the functional groups in the resin matrix, thereby enhancing the compatibility between the resin matrix and the inorganic fillers and improving the overall performance of the material.

[0029] The silane coupling agent forms a stable cross - linked network structure through chemical reactions with the resin. Through the enhancement of this structure, the material can not only improve its mechanical properties and thermal stability but also enhance its flame - retardant performance. The initiator plays a catalytic role in the silane cross - linking reaction, promoting the activation of silane groups and further strengthening the adhesion force of the material.

[0030] Material B includes multiple components such as masterbatch, mLLDPE 4518PA, compatibilizer MC216A, MDH, lubricant silicone, antioxidant 405, plasticizer DOTP, etc. The mLLDPE resin is one of the core components. As a high - crystallinity resin, the higher its crystallinity, the better its oil resistance. The introduction of the mLLDPE resin not only enhances the oil resistance and mechanical strength of the cable sheath but also improves the stability of the material at high temperatures. The high VA content (50 - 70%) of EVA rubber can improve the flexibility of the material and regulate its low - temperature performance.

[0031] The high crystallinity of mLLDPE increases the density of its molecular arrangement, making the material more robust and with stronger high - temperature and oil - resistance capabilities. In addition, the high VA content in EVA rubber improves the low - temperature performance and flexibility of the material, but as the VA content increases, the low - temperature performance will decline to some extent. Therefore, precise control of the VA content in the formulation is particularly important. The main function of compatibilizer MC216A is to improve the compatibility between EVA and mLLDPE, enhance the bonding force between the two, and thus improve the comprehensive performance of the overall material.

[0032] The present invention uses a combination of aluminum hydroxide (ATH) and magnesium hydroxide (MDH) as a halogen-free flame retardant. Both ATH and MDH are halogen-free flame retardants. Through a hydration reaction, they release water vapor at high temperatures, absorb heat, and inhibit flame spread. At the same time, they can reduce the release of toxic gases during combustion. Compared with traditional halogen-based flame retardant materials, aluminum hydroxide and magnesium hydroxide improve the flame retardancy while reducing the release of harmful smoke, enhancing the safety of the material.

[0033] Aluminum hydroxide and magnesium hydroxide release water vapor at high temperatures, playing a role in physical cooling and oxygen isolation, thus effectively inhibiting the spread of flames. The combined use of aluminum hydroxide and magnesium hydroxide can achieve a better flame retardant effect and avoid the problem of generating toxic gases during the combustion of halogen-based flame retardant materials, reducing the negative impact on the environment.

[0034] The functions of the plasticizer (DOTP) and the lubricant (silicone) in the formulation are mainly to adjust the hardness, fluidity, and low-temperature performance of the material. The plasticizer can effectively lower the glass transition temperature of the material, enabling it to maintain a certain degree of flexibility and operability at low temperatures. The lubricant is mainly used to improve the fluidity of the material during processing, reduce friction, lower the processing temperature, and improve production efficiency.

[0035] The plasticizer inserts between polymer chains, increasing the spacing between polymer segments, thus lowering the glass transition temperature of the material and enhancing its flexibility. The lubricant reduces the internal friction of the polymer, reduces heat generation during processing, improves the fluidity of the material, and reduces energy consumption.

[0036] In the preparation process of the present invention, microwave-assisted reactive extrusion technology is used, combined with the action of silane coupling agents, significantly improving the processing performance of the material. Microwave-assisted extrusion technology can accelerate the reaction rate, reduce the heat treatment time, improve production efficiency, while reducing energy consumption and material waste.

[0037] Microwave-assisted reactive extrusion technology can directly heat the material through microwave energy, making the heat distribution during the reaction more uniform, the reaction speed faster, and greatly shortening the reaction time in the traditional production process. In addition, the introduction of microwave technology also improves the uniformity and stability of the reaction, ensuring the high quality of the material.

[0038] A method for preparing a double oil-resistant silane cross-linked flame-retardant polyolefin sheath material for railway locomotives, comprising the following steps: S1. Prepare Material A and Material B according to the formula: Prepare the components of Material A and the components of Material B according to a predetermined ratio, and uniformly mix the required raw materials; S2. Mixing and Reaction: Mix Material A and Material B through a twin-screw extruder and conduct a reaction. Control the temperature at 180 - 220 °C and the reaction time at 30 - 60 min; S3. Silane Crosslinking Process: Use microwave-assisted reactive extrusion technology to conduct a crosslinking reaction at a temperature of 180 - 220 °C for a reaction time of 5 - 15 min to promote the crosslinking reaction between the silane coupling agent and the resin matrix and form a three-dimensional network structure; S4. Molding and Cooling: Mold the reacted mixture and rapidly cool it through a cooling system to ensure the stability of the morphology and physical properties of the final product.

[0039] Example 1: Improving Oil Resistance and Mechanical Strength Raw Material Ratio: Material A: Silane Coupling Agent A - 172: 1.5 parts; Silane Coupling Agent A - 171: 0.8 parts; Initiator: 0.15 parts; Masterbatch: 100 parts; Material B: Color Masterbatch: 16 parts; mLLDPE4518PA: 18 parts; Compatibilizer MC216A: 3 parts; MDH Magnesium Hydroxide: 50 parts; Silicone Lubricant: 0.8 parts; Antioxidant 405: 7 parts; Antioxidant MB: 7 parts; Lubricant Zinc Stearate: 0.8 parts; Silane Coupling Agent A - 172: 0.7 parts; Catalyst: 0.5 parts.

[0040] Process Steps: Prepare Material A and Material B: Mix the silane coupling agent, initiator, and masterbatch of Material A in proportion, and prepare each component of Material B according to the formula ratio.

[0041] Mixing and Reaction: Mix Material A and Material B through a twin-screw extruder, set the temperature at 190 °C, and control the mixing reaction time at 40 min.

[0042] Silane Crosslinking: Use microwave-assisted reactive extrusion technology to conduct a crosslinking reaction at a temperature of 200 °C for a reaction time of 10 min.

[0043] Molding and Cooling: Mold the mixed material flow through a mold, set the cooling time at 5 min, and ensure the stability of the product shape and physical properties.

[0044] Example 2: Improving the Low-Smoke and Halogen-Free Flame Retardant Performance Raw Material Ratio: Material A: Silane Coupling Agent A-172: 1.8 parts Silane Coupling Agent A-171: 0.6 parts Initiator: 0.1 part Masterbatch: 100 parts Material B: Color Masterbatch: 17 parts mLLDPE4518PA: 16 parts Compatibilizer MC216A: 3 parts MDH Magnesium Hydroxide: 55 parts Silicone Lubricant: 0.6 part Antioxidant 405: 6 parts Antioxidant MB: 6 parts Lubricant Zinc Stearate: 0.6 part Silane Coupling Agent A-172: 0.6 part Catalyst: 0.4 part

[0045] Process Steps: Preparation of Material A and Material B: Prepare each component of Material A and Material B according to the formula to ensure that each component is evenly dispersed.

[0046] Mixing and Reaction: Use a twin-screw extruder for mixing, with the temperature controlled at 200°C and the reaction time being 45 min.

[0047] Silane Crosslinking Process: Under the microwave-assisted reactive extrusion technology, the reaction temperature is 210°C and it lasts for 10 min, and a crosslinking reaction occurs between the silane coupling agent and the resin matrix.

[0048] Molding and Cooling: The reacted mixture is fed into a molding machine for rapid cooling, and the cooling time is set to 6 min to ensure the stability of the final molded product.

[0049] Example 3: Optimizing Production Costs and Economic Benefits Raw Material Ratio: Material A: Silane Coupling Agent A-172: 1.5 parts Silane Coupling Agent A-171: 0.7 part Initiator: 0.2 part Masterbatch: 100 parts Material B: Color Masterbatch: 18 parts mLLDPE4518PA: 17 parts Compatibilizer MC216A: 3 parts MDH Magnesium Hydroxide: 52 parts; Silicone Lubricant: 0.7 parts; Antioxidant 405: 6 parts; Antioxidant MB: 6 parts; Lubricant Zinc Stearate: 0.7 parts; Silane Coupling Agent A-172: 0.6 parts; Catalyst: 0.5 parts.

[0050] Process Steps: Batching and Preparation: Prepare each component of Material A and Material B according to the above formula to ensure uniform mixing of the raw materials.

[0051] Mixing and Reaction: Use a twin-screw extruder for mixing and reaction, set the temperature at 185°C, and the reaction time is 35 min.

[0052] Silane Crosslinking Process: Use microwave-assisted reactive extrusion technology to carry out crosslinking reaction at 180°C, the reaction time is 12 min, and a crosslinked structure is formed.

[0053] Molding and Cooling: After molding through a mold, carry out cooling treatment, the cooling time is 7 min, to ensure the stability of the material's properties and form.

[0054] Comparative Example 1 - Changing the Ratio of POE to mLLDPE: Comparative Raw Material Ratio: Material A: Silane Coupling Agent A-172: 1.5 parts; Silane Coupling Agent A-171: 0.7 parts; Initiator: 0.15 parts; Masterbatch: 100 parts; Material B: Color Masterbatch: 16 parts; mLLDPE4518PA: 12 parts (less than the example); POEC5070D: 22 parts (more than the example); Compatibilizer MC216A: 3 parts; MDH Magnesium Hydroxide: 50 parts; Silicone Lubricant: 0.7 parts; Antioxidant 405: 6 parts; Antioxidant MB: 6 parts; Lubricant Zinc Stearate: 0.7 parts; Silane Coupling Agent A-172: 0.6 parts; Catalyst: 0.5 parts.

[0055] Process Steps: Prepare each component of Material A and Material B according to the above formula to ensure uniform mixing of the raw materials.

[0056] Mix Material A and Material B through a twin-screw extruder, set the temperature at 190 °C, and the reaction time at 40 min.

[0057] Use microwave-assisted reactive extrusion technology to carry out cross-linking reaction at 200 °C for 10 min.

[0058] Mold the reacted mixture and rapidly cool it through a cooling system.

[0059] Comparative Example 2 - Change the ratio of aluminum hydroxide (ATH) to magnesium hydroxide (MDH): Compare the raw material ratios: Material A: Silane coupling agent A-172: 1.5 parts; Silane coupling agent A-171: 0.8 parts; Initiator: 0.1 part; Masterbatch: 100 parts; Material B: Color masterbatch: 18 parts mLLDPE4518PA: 16 parts; Compatibilizer MC216A: 3 parts; ATH aluminum hydroxide: 45 parts (decreased compared to the example); MDH magnesium hydroxide: 40 parts (increased compared to the example); Silicone lubricant: 0.6 part; Antioxidant 405: 6 parts; Antioxidant MB: 6 parts; Lubricant zinc stearate: 0.6 part; Silane coupling agent A-172: 0.6 part; Catalyst: 0.4 part.

[0060] Process steps: Prepare each component of Material A and Material B according to the formula to ensure uniform mixing.

[0061] Use a twin-screw extruder to mix and react at a temperature of 195 °C, and set the reaction time at 45 min.

[0062] Adopt microwave-assisted reactive extrusion technology, with a reaction temperature of 205 °C and a duration of 12 min.

[0063] Mold the reacted mixture through a mold and carry out cooling.

[0064] Comparative Example 3 - Use traditional reactive extrusion technology (without using microwave-assisted technology): Comparison of raw material ratios: Material A: Silane coupling agent A-172: 1.6 parts; Silane coupling agent A-171: 0.7 parts; Initiator: 0.2 parts; Masterbatch: 100 parts; Material B: Color masterbatch: 17 parts mLLDPE4518PA: 16 parts; Compatibilizer MC216A: 3 parts; MDH magnesium hydroxide: 55 parts; Silicone lubricant: 0.7 parts; Antioxidant 405: 7 parts; Antioxidant MB: 7 parts; Lubricant zinc stearate: 0.7 parts; Silane coupling agent A-172: 0.7 parts; Catalyst: 0.6 parts.

[0065] Process steps: Prepare Material A and Material B according to the above formula to ensure uniform mixing of the materials.

[0066] Mix Material A and Material B through a twin-screw extruder, set the temperature to 200 °C, and the reaction time to 60 min (without microwave assistance).

[0067] Carry out conventional reactive extrusion without using microwave-assisted technology, and the reaction duration is 15 min.

[0068] The reacted mixture is formed through a mold, and the cooling time is set to 10 min.

[0069] Comparative Example 4 - Using different types of plasticizers (DOS instead of DOTP): Comparison of raw material ratios: Material A: Silane coupling agent A-172: 1.7 parts Silane coupling agent A-171: 0.6 parts Initiator: 0.2 parts Masterbatch: 100 parts Material B: Color masterbatch: 16 parts; mLLDPE4518PA: 17 parts; Compatibilizer MC216A: 3 parts; MDH magnesium hydroxide: 53 parts; Silicone lubricant: 0.6 parts; Antioxidant 405: 6 parts; Antioxidant MB: 6 parts; Lubricant zinc stearate: 0.6 parts; Silane coupling agent A-172: 0.6 parts; Catalyst: 0.5 parts; Plasticizer DOS: 0.8 parts (replacing DOTP).

[0070] Process steps: Prepare Material A and Material B according to the above formula to ensure uniform dispersion of the raw materials.

[0071] Use a twin-screw extruder for mixing, set the temperature at 190 °C, and the reaction time at 45 min.

[0072] Carry out cross-linking reaction under the conventional reactive extrusion process, with the reaction temperature at 200 °C and the duration at 12 min.

[0073] The reacted material is formed and cooled by a molding machine.

[0074] Experimental design description: Experimental purpose: The purpose of this experiment is to verify the effect of the present invention by comparing the examples with the comparative examples, focusing on testing the advantages in aspects such as oil resistance, flame retardancy, mechanical strength, low-temperature performance, and production efficiency, and further proving the creative improvement of the present invention in solving the problems of the existing technology.

[0075] Experimental materials: Example 1: Use the complete formula of the present invention and prepare according to all components and processes in the technical solution.

[0076] Example 2: Similar to Example 1, but different EVMs (VA content 50 - 70%) are used in the masterbatch formula.

[0077] Example 3: Similar to Example 1, but microwave-assisted extrusion technology is adopted during the cross-linking process, and different proportions of flame retardants (different ratios of ATH and MDH) are used.

[0078] Comparative Example 1: In the ratio of Material A and Material B, the ratio of POE to mLLDPE is changed.

[0079] The proportion of POE increases and the proportion of mLLDPE decreases.

[0080] Comparative Example 2: The ratio of ATH and MDH is changed.

[0081] The ratio of ATH and MDH is adjusted to less ATH and more MDH.

[0082] Comparative Example 3: Instead of using microwave-assisted reactive extrusion technology, traditional reactive extrusion technology was adopted, and the reaction time was increased.

[0083] Comparative Example 4: Conventional plasticizers (DOS replaced DOTP) were used.

[0084] Experimental procedures: Formulation preparation and mixing: Prepare Material A and Material B according to the formulations of each example and comparative example, ensuring uniform mixing of the raw materials and avoiding formulation errors.

[0085] Extrusion and reaction: Use a twin-screw extruder for mixing reactions. Set the temperature at 180°C to 220°C and the time at 30 min to 60 min to ensure sufficient mixing.

[0086] Silane cross-linking process: For Examples 1, 2, 3 and Comparative Examples 1, 2, 3, use microwave-assisted reactive extrusion technology to react at a temperature of 200°C for 5 to 15 min to ensure complete cross-linking (Comparative Example 3 uses traditional reactive extrusion technology with the temperature set at 200°C and the reaction time at 20 min).

[0087] Molding and cooling: The reacted mixture is molded through a die. Set the cooling time at 5 to 10 min to ensure the physical form of the material is stable.

[0088] Test items: Oil resistance test: Immerse the samples in the oil and measure the volume expansion rate, hardness change, and surface aging degree.

[0089] Flame retardancy test: Conduct a combustion test according to the UL94 standard to evaluate the flame spread rate, smoke release amount, etc.

[0090] Mechanical property test: Conduct a tensile test to measure parameters such as tensile strength and elongation at break.

[0091] Low-temperature property test: Under low-temperature conditions, test the brittleness of the samples and evaluate the flexibility in a low-temperature environment.

[0092] Experimental data: Sample number Oil resistance (volume expansion rate) Flame retardancy (UL94 rating) Tensile strength (MPa) Elongation at break (%) Low temperature flexibility (low temperature brittleness) Example 1 5% V-0 28 450 No brittleness Example 2 6% V-0 27 440 No brittleness Example 3 5% V-0 29 460 No brittleness Comparative example 1 10% V-2 25 430 Slight brittleness Comparative example 2 9% V-1 24 420 Obvious brittleness Comparative example 3 12% V-2 23 410 Obvious brittleness Comparative example 4 11% V-2 22 400 Obvious brittleness Experimental summary: The results of this experiment show that the performance of the examples is significantly better than that of all comparative examples. The oil resistance, flame retardancy, and mechanical strength of Examples 1, 2, and 3 are significantly higher than those of the comparative examples, and no brittleness occurs at low temperatures, indicating their excellent low-temperature flexibility. In particular, Example 3, using microwave-assisted reactive extrusion technology and an optimized ratio of ATH to MDH, achieves optimal flame retardancy and mechanical properties.

[0093] Mechanistically, the combination of highly crystalline mLLDPE and EVA rubber with a high VA content significantly enhances the oil resistance and mechanical strength of the sheath. The cross-linking process of the silane coupling agent strengthens the molecular structure between materials, making it more compact and avoiding the expansion problem of the sheath after immersion in oil. The introduction of a halogen-free flame retardant (ATH and MDH used in combination) not only improves the flame retardancy but also significantly reduces the toxic gases generated during combustion, enhancing safety.

[0094] From the perspective of production cost, the use of microwave-assisted reactive extrusion technology not only shortens the reaction time but also improves production efficiency. Compared with traditional technologies, it reduces energy consumption and material waste, demonstrating obvious economic benefits. This optimized process effectively improves the overall performance of the material and has good prospects for industrial application.

[0095] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A double oil-resistant and silane-crosslinked flame-retardant polyolefin sheath material for railway locomotives, characterized in that, By weight, it consists of the following raw materials: Material A: Silane coupling agent A-172: 1-2 parts; Silane coupling agent A-171: 0.5-1 part; Initiator: 0.1-0.2 part; Masterbatch: 100 parts; Material B: Color masterbatch: 15-20 parts; mLLDPE4518PA: 15-20 parts; Compatibilizer MC216A: 2-5 parts; MDH: 40-60 parts; Silicone lubricant: 0.5-1 part; Antioxidant 405: 5-10 parts; Antioxidant MB: 5-10 parts; Lubricant zinc stearate: 0.5-1 part; Silane coupling agent A-172: 0.5-0.8 part; Catalyst: 0.2-0.6 part.

2. The double oil-resistant silane cross-linked flame-retardant polyolefin sheath material for railway locomotives according to claim 1, wherein The mass ratio of Material A to Material B is 90-92:10-8.

3. The double oil-resistant and silane-crosslinked flame-retardant polyolefin sheath material for railway locomotives according to claim 1, characterized in that The masterbatch is prepared from the following components by weight: POEC5070D: 5-10 parts; EVM700XL: 2-5 parts; mLLDPE3518CB: 20-25 parts; Compatibilizer MC216A: 3-5 parts; ATH aluminum hydroxide: 40-50 parts; MDH magnesium hydroxide: 10-15 parts; Silicone rubber: 2-5 parts; Antioxidant: 0.2-0.4 part; Copper inhibitor: 0.1-0.3 part; Plasticizer: 0.5-1.0 part; Dispersant: 0.2-0.4 part; Silane coupling agent A-172: 0.3-0.6 part.

4. The double oil-resistant and silane-crosslinked flame-retardant polyolefin sheath material for railway locomotives according to claim 3, wherein The EVM rubber can use a VA content of 50-70%.

5. The double oil-resistant silane-crosslinked flame-retardant polyolefin sheath material for railway locomotives according to claim 1, characterized in that The compatibilizer is maleic anhydride grafted polyethylene compatibilizer or maleic anhydride grafted ethylene vinyl acetate compatibilizer.

6. The double oil-resistant and silane-crosslinked flame-retardant polyolefin sheath material for railway locomotives according to claim 3, wherein The ATH aluminum hydroxide and MDH magnesium hydroxide are both inorganic flame retardants, and the silicone rubber is vinyl silicone rubber with a vinyl content of 1-5%.

7. The double oil-resistant and silane-crosslinked flame-retardant polyolefin sheath material for railway locomotives according to claim 3, characterized in that, The antioxidant is 1010 or 1076, the copper inhibitor is 1024 or MD-5, the plasticizer is DOTP or DOS, the dispersant is EBS or polyethylene wax, and the silane coupling agent is A-172 or A-151.

8. The double oil-resistant silane cross-linked flame-retardant polyolefin sheath material for railway locomotives according to claim 3, wherein The POE can be either DOW8200 or Mitsui DF840, with a melt index of 2-5 g / 10 min and a Shore hardness A of 70-80. The mLLDPE can be either 3812PA or SP2520, with a melt index of 2-10 g / 10 min and a crystallinity of 60-70%.

9. Preparation method of double oil-resistant and silane-crosslinked flame-retardant polyolefin sheath material for railway locomotives, characterized in that, It includes the following steps: S1. Prepare Material A and Material B according to the formula: Prepare the components of Material A and the components of Material B according to the predetermined ratio, and uniformly mix the required raw materials; S2. Mixing and reaction: Mix Material A and Material B through a twin-screw extruder and carry out the reaction, with the temperature controlled at 180-220 °C and the reaction time being 30-60 min; S3. Silane cross-linking process: Use microwave-assisted reactive extrusion technology to carry out the cross-linking reaction at a temperature of 180-220 °C for a reaction time of 5-15 min to promote the cross-linking reaction between the silane coupling agent and the resin matrix and form a three-dimensional network structure; S4. Molding and cooling: Mold the reacted mixture and quickly cool it through a cooling system to ensure the stability of the final product's form and physical properties.

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