Water-blocking cable sheath material and preparation method thereof

Abstract

The invention discloses a water-blocking cable sheath material and a preparation method thereof, the sheath material adopts polyester type TPU and EVA as matrix resin, and the sheath material is prepared through specific processes including functionalization pretreatment, step-by-step functional master batch construction, dynamic crosslinking and irradiation crosslinking. The preparation method is characterized by comprising the following steps: firstly, respectively preparing the functionalized TPU and the silane modified EVA to improve the compatibility; then preparing a functionalized nano composite water-blocking agent and a pre-dispersed flame-retardant master batch; then preparing elastomer master batches containing the interface anchoring water blocking agent through a dynamic vulcanization technology; and finally, blending and extruding all the components, and carrying out irradiation treatment. A stable'sea-island 'structure and a three-dimensional cross-linked network are formed inside the obtained sheath material, so that the oxygen index of the sheath material is larger than or equal to 30%, the tensile strength is larger than or equal to 16 MPa, the elongation at break is larger than or equal to 300%, the water absorption capacity of the sheath material soaked in a 50-meter water column for 30 days is smaller than or equal to 8 mg / cm < 2 >, the sheath material is free of cracking when bent at the low temperature of-40 DEG C, the comprehensive performance is excellent, and the sheath material is particularly suitable for severe environments such as ocean engineering, mobile robot drag chains and photovoltaic cables.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically, it relates to a water-blocking cable sheath material and its preparation method. Background Technology

[0002] With the rapid development of marine engineering, mobile robot cable chain systems, and photovoltaic power plants, unprecedentedly high demands are being placed on the comprehensive performance of cable sheath materials. These demanding applications not only require materials to possess excellent flame retardancy (OI ≥ 30%) and mechanical strength (tensile strength ≥ 16 MPa), but also to maintain extremely low water absorption (e.g., ≤ 8 mg / cm³) under complex environments such as long-term high water pressure and low-temperature cycling. 2 It has stable low-temperature toughness (no cracking at -40℃).

[0003] To address this challenge, polyester-based thermoplastic polyurethane (TPU) is often considered as a matrix resin for high-performance sheathing materials due to its excellent mechanical strength, abrasion resistance, and oil resistance. However, TPU itself has poor flame retardancy and is expensive to use alone. Ethylene-vinyl acetate copolymer (EVA), on the other hand, is considered an ideal candidate for blending with TPU to balance performance and cost due to its excellent flexibility, low price, and inherent flame retardant potential. Nevertheless, existing simple TPU / EVA blending systems still face many insurmountable technical bottlenecks: First, there is the contradiction between compatibility and long-term stability. TPU and EVA are thermodynamically incompatible systems, and simple physical blending will lead to severe phase separation, forming a fragile interface. Under long-term use, especially under humid heat, water pressure, or mechanical stress, moisture and stress can easily penetrate and concentrate along this weak interface, resulting in a sharp decline in water-blocking performance and a rapid decrease in mechanical strength.

[0004] Secondly, there is the challenge of synergistic dispersion and positioning of multifunctional components. This manifests in two ways: First, nanoscale water-blocking agents added to achieve long-lasting water resistance are prone to agglomeration at the interface of incompatible phases, failing to form an effective water-blocking barrier and instead becoming stress concentration points. Second, inorganic flame-retardant fillers added in large quantities to achieve high flame retardancy are difficult to ensure uniform distribution in both the TPU and EVA phases in traditional processes, leading to localized flame-retardant failure. More importantly, water-blocking agents need to accumulate at the interface to block water molecule pathways, while flame retardants need to be uniformly distributed throughout the matrix to construct a complete insulation layer. These two opposing distribution requirements cannot be simultaneously achieved in a one-pot blending process, resulting in shortcomings in material performance.

[0005] Therefore, there is an urgent need in this field for an innovative technical solution that can fundamentally solve the compatibility problem between TPU and EVA by starting with molecular design and microstructure control. Through a clever step-by-step process design, pre-dispersed flame retardant masterbatch and dynamic cross-linked masterbatch containing interface anchoring water-blocking agent can be constructed separately. Ultimately, the precise anchoring of water-blocking components at the phase interface and the uniform dispersion of flame retardant components in the whole matrix can be achieved, thereby preparing cable sheath material with long-lasting water blocking, high strength and toughness, high flame retardancy and excellent processability. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a water-blocking cable sheath material and its preparation method.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows: A method for preparing a water-blocking cable sheath material includes the following steps: (1) Polyester-type thermoplastic polyurethane (TPU) and maleic anhydride grafts accounting for 1-3% of its mass are premixed in a high-speed mixer at 80-90°C for 5-10 minutes to obtain functionalized TPU; ethylene-vinyl acetate copolymer (EVA) and vinyltriethoxysilane accounting for 0.5-1.5% of its mass are premixed under the same conditions to obtain silane-modified EVA; (2) The nano-sized montmorillonite was calcined at 550~600℃ for 1~1.5 hours, cooled, and then dry-modified with 2~4% of its mass titanate coupling agent in a high-speed mixer at 100~110℃ for 10~15 minutes to obtain modified nano-montmorillonite; the modified nano-montmorillonite, liquid fluorocarbon resin, and nano alumina were added to an aqueous acrylic emulsion at a mass ratio of (4~5):(1.2~1.8):(1.5~2), and sheared at 50~60℃ for 15~25 minutes with a high-speed shear machine at 4000~6000 rpm to form a composite emulsion; then spray-dried to obtain a powdered functionalized nano-composite water-blocking agent; (3) Add magnesium hydroxide, microcapsule red phosphorus, nano silica, silicone powder and the silane-modified EVA obtained in step (1) into a twin-screw extruder, control the temperature at 120~140℃, melt blend and then granulate to obtain pre-dispersed flame retardant masterbatch. (4) The functionalized TPU obtained in step (1), the remaining silane-modified EVA, epoxidized soybean oil, crosslinking agent triallyl isocyanurate and zinc stearate are added to a mixer and blended at 140~150℃ and 50~70 rpm. The functionalized nanocomposite water-blocking agent obtained in step (2) is added and the mixture is continued for 2~4 minutes. When the temperature or power value of the system material reaches the peak and begins to decrease, a composite crosslinking agent composed of benzoyl peroxide and accelerator DM at a mass ratio of 1:(0.1~0.3) is added and the mixture is continued for 6~10 minutes at the same temperature to carry out the dynamic crosslinking reaction. After the reaction is completed, the material is quickly discharged, cooled and crushed to obtain the dynamic crosslinked elastomer masterbatch. (5) The dynamic cross-linked elastomer masterbatch obtained in step (4), the pre-dispersed flame retardant masterbatch obtained in step (3), polycarbonate, and lubricant EBS are fed into a twin-screw extruder. The temperature of each section is controlled within the range of 150~160℃, the screw speed is 200~300 rpm, vacuum devouring is performed, and the melt is cooled and pelletized to obtain sheath material granules. (6) The sheath material particles obtained in step (5) are irradiated by an irradiation accelerator with an irradiation dose of 5~15kGy.

[0008] Furthermore, in step (1), the maleic anhydride graft is a maleic anhydride-grafted polyolefin elastomer. By limiting the maleic anhydride graft to a maleic anhydride-grafted polyolefin elastomer, it exhibits excellent compatibility with functionalized TPU, effectively promoting interfacial bonding and significantly enhancing the impact toughness and low-temperature toughness of the blend material as an elastomer.

[0009] Further, in step (2), the functionalized nanocomposite water-blocking agent is composed of the following components by weight: 35-45 parts modified nano-montmorillonite, 10-15 parts liquid fluorocarbon resin, 12-18 parts nano-alumina, and 30-40 parts water-based acrylic emulsion. By optimizing the specific composition and ratio of the functionalized nanocomposite water-blocking agent, a dense "physical maze-chemical hydrophobic-nanofilled" synergistic water-blocking layer is formed among the modified nano-montmorillonite, liquid fluorocarbon resin, and nano-alumina, maximizing the water-blocking efficiency.

[0010] Furthermore, in step (3), the total amount of the composite crosslinking agent added accounts for 1.0~2.0% of the total mass of the functionalized TPU and silane-modified EVA. By precisely controlling the amount of composite crosslinking agent added, the degree of dynamic crosslinking reaction is ensured to be moderate, which can form a sufficient number of crosslinking points to stabilize the microstructure, while avoiding material embrittlement caused by excessive crosslinking, thus perfectly balancing strength and toughness.

[0011] Furthermore, the amount of the functionalized nanocomposite water-blocking agent obtained in step (2) accounts for 10-18% of the total mass of the sheath material; the amount of the pre-dispersed flame-retardant masterbatch obtained in step (3) accounts for 25-35% of the total mass of the sheath material. By limiting the ratio of the functionalized nanocomposite water-blocking agent to the pre-dispersed flame-retardant masterbatch, while ensuring the ultimate water-blocking and flame-retardant performance, the problems of deteriorated processing fluidity, decreased mechanical properties and excessive cost caused by excessive filler are avoided, thus achieving the best balance between performance and cost.

[0012] The present invention also provides a water-blocking cable sheath material, which is prepared by the above-mentioned preparation method. The raw materials used include, by weight, 70-80 parts of polyester thermoplastic polyurethane, 30-40 parts of ethylene-vinyl acetate copolymer, 15-20 parts of magnesium hydroxide, 5-8 parts of microencapsulated red phosphorus, 10-15 parts of epoxidized soybean oil, 1-1.5 parts of crosslinking agent triallyl isocyanurate, 2-3 parts of zinc stearate, 3-4 parts of liquid fluorocarbon resin, 1-2 parts of lubricant EBS, 5-7 parts of polycarbonate, 8-10 parts of nano-montmorillonite, 3-5 parts of nano-alumina, 6-8 parts of water-based acrylic emulsion, 4-6 parts of silicone powder, 0.7-2.4 parts of maleic anhydride-grafted polyolefin elastomer, and 0.15-0.6 parts of vinyltriethoxysilane. By defining the precise weight ratio of each raw material component, the molecular design ensures that each component can fully perform its design function and achieves the best balance between cost and performance, so that the sheath material can meet the stringent performance requirements and has the economic feasibility for large-scale industrialization.

[0013] Furthermore, the sheath material contains cross-linked polyester-type thermoplastic polyurethane microdomains with a size of 2-8 μm formed by dynamic cross-linking, and a functionalized nanocomposite water-blocking agent anchored at the interface between the microdomains and the ethylene-vinyl acetate copolymer matrix; the sheath material as a whole has a three-dimensional cross-linked network induced by radiation cross-linking. This unique microstructure is the core of the invention, and it is the fundamental reason why the material simultaneously achieves high strength, high toughness, long-lasting water resistance, and high flame retardancy, which is the decisive characteristic that makes its performance surpass that of conventional blended materials.

[0014] Furthermore, the sheath material has an oxygen index ≥30%, tensile strength ≥16MPa, elongation at break ≥300%, and water absorption ≤8mg / cm³ after immersion in 50-meter water column pressure for 30 days. 2 By setting clear and unconventional performance indicators, the groundbreaking technological advancements achieved by the present invention are quantified and demonstrated, providing a clear and reliable performance guarantee for its application in the high-end market.

[0015] Furthermore, after bending the sheath material 180° around a cylinder with a diameter five times the outer diameter of the cable at a low temperature of -40°C, no cracks appeared on the surface. This fully verifies the excellent low-temperature toughness of the sheath material, ensuring its long-term reliability in application scenarios such as photovoltaic power plants and mobile robots in cold regions, high altitudes, or large day-night temperature differences.

[0016] Compared with the prior art, the present invention has the following beneficial effects: I. This invention significantly improves the compatibility and interfacial stability of the matrix resin. By functionalizing TPU with maleic anhydride and modifying EVA with silane, reactive active groups are introduced into the originally incompatible phases. In the subsequent dynamic crosslinking reaction, these groups participate in the reaction, forming chemical bonds at the interface between the two phases, elevating simple physical blending to chemical compatibilization. This effectively inhibits phase separation, forming a firmly bonded sea-island structure, thereby enhancing the material's ability to resist permeation and maintain mechanical properties under harsh environments such as humidity, heat, and water pressure.

[0017] II. This invention achieves the synergistic design and precise construction of water-blocking and flame-retardant functions at the microscale by prefabricating functionalized nanocomposite water-blocking agents and pre-dispersed flame-retardant masterbatches through independent steps. This step-by-step construction strategy allows the water-blocking agent to be selectively anchored at the TPU-EVA interface during the dynamic cross-linking step, directly forming an effective barrier along the critical pathway of water penetration. Simultaneously, the flame-retardant, through pre-melt blending with a portion of the EVA matrix, ensures a more uniform distribution in the final product, contributing to the formation of a continuous and dense flame-retardant char layer. This design successfully solves the technical challenges of uncontrollable functional component distribution and mutual interference in traditional blending processes.

[0018] Third, this invention constructs a multi-layered, dual cross-linking network, comprehensively improving the material's durability. Dynamic cross-linking forms micro-crosslinking points within the polyester-type TPU phase and at the interface between the two phases, endowing the material with excellent initial mechanical strength and elasticity. Subsequent electron irradiation cross-linking establishes a three-dimensional network that runs through the entire material matrix based on the already formed microstructure. This synergistic effect of chemical cross-linking and radiation cross-linking jointly enhances the material's resistance to heat deformation, creep resistance, and long-term shape stability, making it more suitable for applications with stringent durability requirements. Detailed Implementation

[0019] The specific embodiments are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise specified, the raw materials and reagents used in the examples are commercially available.

[0020] Example 1 This embodiment provides a water-blocking cable sheath material and its preparation method: (1) Weigh 75 kg of polyester thermoplastic polyurethane (TPU) and premix it with 2% (i.e. 1.5 kg) of maleic anhydride grafted polyolefin elastomer (POE-g-MAH) in a high-speed mixer at 85°C for 8 minutes to obtain functionalized TPU; weigh 35 kg of ethylene-vinyl acetate copolymer (EVA) and premix it with 1% (i.e. 0.35 kg) of vinyltriethoxysilane in a high-speed mixer at 85°C for 8 minutes to obtain silane modified EVA.

[0021] (2) Weigh 8 kg of nano-sized montmorillonite, calcine it at 665℃ for 1.7 hours, cool it, and then dry-modify it for 12 minutes at 105℃ with 3% (i.e., 0.24 kg) of titanate coupling agent in a high-speed mixer to obtain modified nano-montmorillonite. Add the above modified nano-montmorillonite, 3.6 kg of liquid fluorocarbon resin, and 4 kg of nano-alumina to 7 kg of water-based acrylic emulsion, and shear it at 55℃ for 22 minutes with a high-speed shear machine at 5500 rpm to form a composite slurry. Then spray-dry the slurry to obtain a powdered functionalized nano-composite water-blocking agent with a total weight of about 22.6 kg.

[0022] (3) Weigh 17 kg of magnesium hydroxide, 6.5 kg of microcapsule red phosphorus, 2 kg of nano silica, and 5 kg of silicone powder, and add them together with 15 kg of silane-modified EVA obtained in step (1) into a twin-screw extruder. Control the temperature at 130°C, melt-blend and granulate to obtain pre-dispersed flame retardant masterbatch with a total weight of about 45.5 kg.

[0023] (4) Add all the functionalized TPU (76.5 kg) obtained in step (1), the remaining 20 kg of silane-modified EVA obtained in step (1), 12.5 kg of epoxidized soybean oil, 1.3 kg of crosslinking agent triallyl isocyanurate (TAIC) and 2.5 kg of zinc stearate to a mixer and blend them at 145°C and 60 rpm. Add all the functionalized nanocomposite water-blocking agent (about 22.6 kg) obtained in step (2) and continue mixing for 3 minutes. When the power value of the system reaches its peak and begins to decrease, add 1.8 kg of composite crosslinking agent (composed of 1.38 kg of benzoyl peroxide (BPO) and 0.42 kg of accelerator DM) and continue mixing for 9 minutes at the same temperature to carry out dynamic crosslinking reaction. After the reaction is completed, discharge the material quickly, cool and crush it to obtain dynamic crosslinked elastomer masterbatch.

[0024] (5) All the dynamically cross-linked elastomer masterbatch obtained in step (4), 30 kg of pre-dispersed flame retardant masterbatch obtained in step (3), 6 kg of polycarbonate, and 1.5 kg of lubricant EBS are fed into a twin-screw extruder. The temperature of each section of the extruder is controlled within the range of 155℃, the screw speed is 280 rpm, vacuum devolatilization is performed, and the melt is cooled in a water bath, air-dried, and then pelletized to obtain sheath material granules.

[0025] (6) The sheath material particles obtained in step (5) are irradiated by an irradiation accelerator with an irradiation dose of 10 kGy to obtain the water-blocking cable sheath material.

[0026] Example 2 This embodiment provides a water-blocking cable sheath material and its preparation method: (1) Weigh 70 kg of polyester thermoplastic polyurethane (TPU) and premix it with 1% (i.e. 0.7 kg) of maleic anhydride grafted polyolefin elastomer (POE-g-MAH) in a high-speed mixer at 80°C for 10 minutes to obtain functionalized TPU; weigh 30 kg of ethylene-vinyl acetate copolymer (EVA) and premix it with 0.5% (i.e. 0.15 kg) of vinyltriethoxysilane in a high-speed mixer at 80°C for 10 minutes to obtain silane modified EVA.

[0027] (2) Weigh 6 kg of nano-sized montmorillonite, calcine it at 550℃ for 2 hours, cool it, and then dry-modify it for 15 minutes at 100℃ with 2% (i.e., 0.12 kg) of titanate coupling agent in a high-speed mixer to obtain modified nano-montmorillonite. Add the above modified nano-montmorillonite, 2.4 kg of liquid fluorocarbon resin, and 3 kg of nano-alumina to 5 kg of water-based acrylic emulsion, and shear it at 50℃ for 25 minutes with a high-speed shear machine at 4000 rpm to form a composite slurry. Then spray-dry the slurry to obtain a powdered functionalized nano-composite water-blocking agent with a total weight of about 16.5 kg.

[0028] (3) Weigh 15 kg of magnesium hydroxide, 5 kg of microcapsule red phosphorus, 1.5 kg of nano silica and 4 kg of silicone powder, and add them together with 12 kg of silane-modified EVA obtained in step (1) into a twin-screw extruder. Control the temperature at 120°C, melt-blend and granulate to obtain pre-dispersed flame retardant masterbatch with a total weight of about 37.5 kg.

[0029] (4) Add all the functionalized TPU (70.7 kg) obtained in step (1), the remaining 18 kg of silane-modified EVA obtained in step (1), 10 kg of epoxidized soybean oil, 1 kg of crosslinking agent TAIC and 3 kg of zinc stearate to a mixer and blend and melt them at 140°C and 50 rpm. Add all the functionalized nanocomposite water-blocking agent (about 16.5 kg) obtained in step (2) and continue to mix for 2 minutes. When the temperature of the system material reaches its peak and begins to decrease, add 1.2 kg of composite crosslinking agent (composed of 1.0 kg of benzoyl peroxide (BPO) and 0.2 kg of accelerator DM) and continue to mix for 6 minutes at the same temperature to carry out dynamic crosslinking reaction. After the reaction is completed, quickly discharge, cool and crush to obtain dynamic crosslinked elastomer masterbatch.

[0030] (5) All the dynamic crosslinked elastomer masterbatch obtained in step (4), 25 kg of pre-dispersed flame retardant masterbatch obtained in step (3), 5 kg of polycarbonate, and 1 kg of lubricant EBS are fed into a twin-screw extruder. The temperature of each section of the extruder is controlled within the range of 150℃, the screw speed is 200 rpm, vacuum devolatilization is performed, and the melt is cooled in a water bath, air-dried, and then pelletized to obtain sheath material granules.

[0031] (6) The sheath material particles obtained in step (5) are irradiated by an irradiation accelerator with an irradiation dose of 5 kGy to obtain the water-blocking cable sheath material.

[0032] Example 3 This embodiment provides a water-blocking cable sheath material and its preparation method: (1) Weigh 80 kg of polyester thermoplastic polyurethane (TPU) and premix it with 3% (i.e. 2.4 kg) of maleic anhydride grafted polyolefin elastomer (POE-g-MAH) in a high-speed mixer at 90°C for 5 minutes to obtain functionalized TPU; weigh 40 kg of ethylene-vinyl acetate copolymer (EVA) and premix it with 1.5% (i.e. 0.6 kg) of vinyltriethoxysilane in a high-speed mixer at 90°C for 5 minutes to obtain silane modified EVA.

[0033] (2) Weigh 10 kg of nano-sized montmorillonite, calcine it at 600℃ for 1.5 hours, cool it, and then dry-modify it for 10 minutes at 110℃ with 4% (i.e., 0.4 kg) of titanate coupling agent in a high-speed mixer to obtain modified nano-montmorillonite. Add the above modified nano-montmorillonite, 4.5 kg of liquid fluorocarbon resin, and 6 kg of nano-alumina to 8 kg of waterborne acrylic emulsion, and shear it at 60℃ for 20 minutes with a high-speed shear machine at 6000 rpm to form a composite slurry. Then spray-dry the slurry to obtain a powdered functionalized nano-composite water-blocking agent with a total weight of about 28.9 kg.

[0034] (3) Weigh 20 kg of magnesium hydroxide, 8 kg of microcapsule red phosphorus, 2.5 kg of nano silica and 6 kg of silicone powder, and add them together with 18 kg of silane-modified EVA obtained in step (1) into a twin-screw extruder. Control the temperature at 140°C, melt-blend and granulate to obtain pre-dispersed flame retardant masterbatch with a total weight of about 54.5 kg.

[0035] (4) Add all the functionalized TPU (82.4 kg) obtained in step (1), the remaining 22 kg of silane-modified EVA obtained in step (1), 15 kg of epoxidized soybean oil, 1.5 kg of crosslinking agent TAIC and 2 kg of zinc stearate to a mixer and blend them at 150°C and 70 rpm. Add all the functionalized nanocomposite water-blocking agent (about 28.9 kg) obtained in step (2) and continue mixing for 4 minutes. When the power value of the system reaches its peak and begins to decrease, add 2.4 kg of composite crosslinking agent (composed of 1.71 kg of benzoyl peroxide (BPO) and 0.69 kg of accelerator DM) and continue mixing for 12 minutes at the same temperature to carry out dynamic crosslinking reaction. After the reaction is completed, discharge the material quickly, cool and crush it to obtain dynamic crosslinked elastomer masterbatch.

[0036] (5) All the dynamic crosslinked elastomer masterbatch obtained in step (4), 35 kg of pre-dispersed flame retardant masterbatch obtained in step (3), 7 kg of polycarbonate, and 2 kg of lubricant EBS are fed into a twin-screw extruder. The temperature of each section of the extruder is controlled within the range of 160℃, the screw speed is 300 rpm, vacuum devolatilization is performed, and the melt is cooled in a water bath, air-dried, and then pelletized to obtain sheath material granules.

[0037] (6) The sheath material particles obtained in step (5) are irradiated by an irradiation accelerator with an irradiation dose of 15 kGy to obtain the water-blocking cable sheath material.

[0038] Comparative Example 1 (Traditional Simple Blending Method) This comparative example uses a traditional one-time blending process without functionalization pretreatment, dynamic crosslinking, or irradiation crosslinking.

[0039] Preparation method: (1) Add 75 kg of polyester thermoplastic polyurethane (TPU), 35 kg of ethylene-vinyl acetate copolymer (EVA), 1.5 kg of maleic anhydride grafted polyolefin elastomer (POE-g-MAH), 0.35 kg of vinyltriethoxysilane, 12.5 kg of epoxidized soybean oil, 1.3 kg of crosslinking agent TAIC, 2.5 kg of zinc stearate, 3.6 kg of liquid fluorocarbon resin, 6 kg of polycarbonate, 1.5 kg of lubricant EBS, 8 kg of nano-grade montmorillonite, 17 kg of magnesium hydroxide, 6.5 kg of microencapsulated red phosphorus, 2 kg of nano-silica, 5 kg of silicone powder, 7 kg of water-based acrylic emulsion, and 4 kg of nano-alumina to a high-speed mixer and mix evenly.

[0040] (2) The mixed material is directly fed into the twin-screw extruder, the temperature of each section is controlled within the range of 155℃, the screw speed is 280 rpm, the melt is cooled in a water bath and dried in the air before being pelletized to obtain the comparison sample.

[0041] Comparative Example 2 (without dynamic vulcanization and irradiation crosslinking) This comparative example retains the functionalization pretreatment and stepwise masterbatch preparation steps, but eliminates the core dynamic crosslinking reaction and subsequent irradiation crosslinking.

[0042] Preparation method: (1) Preparation of functionalized TPU and silane modified EVA: Same as step (1) in Example 1.

[0043] (2) Preparation of functionalized nanocomposite water-blocking agent: Same as step (2) in Example 1.

[0044] (3) Preparation of pre-dispersed flame retardant masterbatch: Same as step (3) in Example 1.

[0045] (4) Preparation of uncrosslinked elastomer masterbatch: All the functionalized TPU (76.5 kg) obtained in step (1), the remaining 20 kg of silane-modified EVA obtained in step (1), 12.5 kg of epoxidized soybean oil, 1.3 kg of TAIC, and 2.5 kg of zinc stearate were added to a mixer and blended and melted for 8 minutes at 145°C and a rotor speed of 60 rpm. All the functionalized nanocomposite water-blocking agent (approximately 22.6 kg) obtained in step (2) were added, and the mixture was further blended for 3 minutes. Without adding composite crosslinking agent, the mixture was directly discharged, cooled, and crushed to obtain uncrosslinked elastomer masterbatch.

[0046] (5) Final blending and granulation: Same as step (5) in Example 1.

[0047] (6) No irradiation crosslinking treatment is performed.

[0048] Comparative Example 3 (without step-by-step construction process) This comparative example abandons the stepwise construction strategy of functional masterbatch, and blends water-blocking agent and flame retardant with all matrix resins in one go, and attempts to achieve dynamic crosslinking.

[0049] Preparation method: (1) Preparation of functionalized TPU and silane modified EVA: Same as step (1) in Example 1.

[0050] (2) All the functionalized TPU (76.5 kg), all the silane-modified EVA (35.35 kg), 12.5 kg of epoxidized soybean oil, 1.3 kg of TAIC, 2.5 kg of zinc stearate, and the corresponding amounts of nano-sized montmorillonite (8 kg), liquid fluorocarbon resin (3.6 kg), nano-alumina (4 kg), water-based acrylic emulsion (7 kg), magnesium hydroxide (17 kg), microencapsulated red phosphorus (6.5 kg), nano-silica (2 kg), silicone powder (5 kg), polycarbonate (6 kg), and lubricant EBS (1.5 kg) obtained in step (1) were added into a mixer and blended and melted at 145°C and a rotor speed of 60 rpm.

[0051] (3) When the power value of the system reaches its peak and begins to decrease, add 1.8 kg of composite crosslinking agent (composed of 1.38 kg of benzoyl peroxide (BPO) and 0.42 kg of accelerator DM), and continue to mix for 9 minutes at the same temperature to carry out dynamic crosslinking reaction. After the reaction is completed, discharge, cool and crush.

[0052] (4) The material obtained in step (3) is fed into a twin-screw extruder for granulation, and the control conditions are the same as in step (5) of Example 1.

[0053] (5) The granulated particles are subjected to irradiation treatment with an irradiation dose of 10 kGy.

[0054] Performance comparison tests were conducted on Examples 1-3 and Comparative Examples 1-3, and the test methods are as follows: 1. Oxygen Index Method: Based on GB / T 2406.2 standard.

[0055] Brief Description: The sample is vertically fixed in a transparent combustion chamber, and a controlled oxygen-nitrogen mixture is introduced from the bottom. The top of the sample is ignited, and the minimum oxygen volume percentage concentration required to maintain stable combustion of the material is measured by adjusting the oxygen concentration. The higher this value, the more difficult the material is to burn.

[0056] 2. Tensile strength and elongation at break Method: Based on GB / T 1040.1 standard.

[0057] Brief Description: The material is made into a standard dumbbell-shaped specimen and fixed on the fixture of a universal testing machine. The specimen is stretched at a constant speed until it breaks. The tensile strength is calculated by dividing the maximum tensile force at fracture by the original cross-sectional area of ​​the specimen. Elongation at break is the ratio of the elongation between the gauges at fracture to the original gauge length, expressed as a percentage, reflecting the toughness of the material.

[0058] 3. Water absorption Methods: Based on the principles of GB / T 1034 for the determination of water absorption of plastics, combined with the immersion test in the cable industry.

[0059] Brief Description: The sample of specified dimensions is completely immersed in distilled water at (23±2)℃, and an equivalent hydrostatic pressure of 50 meters of water column is applied. After soaking for 30 days, the sample is removed, the surface moisture is wiped dry, and the sample is weighed accurately. The water absorption is calculated by dividing the mass difference before and after soaking by the total surface area of ​​the sample.

[0060] 4. Bending at -40℃ Method: Based on GB / T 2951.14 standard.

[0061] Brief Description: The sample is placed in a -40°C cryogenic chamber for a specified time to reach thermal equilibrium. Then, it is quickly bent 180° around a cylinder with a diameter equal to five times the outer diameter of the cable in a cryogenic environment. The surface of the bent portion of the sample is observed visually or with corrected vision for cracks, fissures, or damage.

[0062] 5. Interfacial bonding force: Method: Micromechanical testing method (non-standard routine test, often used for mechanism research).

[0063] Brief Description: Ultrathin slices were prepared, and the stress required for the TPU microregions to detach from the EVA matrix at the interface was precisely measured using equipment such as a nanoindenter or a micro-tensile stage on a micro-mechanical testing instrument. This data is directly used to quantitatively characterize the bonding strength and stability of the "sea-island" structure interface.

[0064] The test results are shown in the table below: Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Oxygen index (%) 33.5 31.2 34.1 26.8 29.5 30.1 Tensile strength (MPa) 19.2 17.1 18.8 11.5 14.3 15.7 Elongation at break (%) 380 325 365 180 260 295 <![CDATA[Water absorption (mg / cm 2 )]]> 4.2 6.8 5.1 22.5 12.7 9.5 -40℃ bending No cracks No cracks No cracks Severe cracking minor cracks microcracks Interfacial bonding force (MPa) 8.5 7.1 8.2 1.8 4.3 5.6 Analysis of the table data yields the following: All performance indicators of Comparative Example 1 (conventional blend) were significantly inferior to those of the embodiments of the present invention. Its water resistance (water absorption 22.5 mg / cm³) was particularly poor. 2The TPU / EVA composite exhibited severely insufficient mechanical properties (tensile strength 11.5 MPa) and cracked at low temperatures, directly demonstrating that the traditional "one-pot method" cannot solve the fundamental problems of poor TPU / EVA compatibility and uneven dispersion of multifunctional components. This highlights the necessity and superior effect of the "stepwise construction" process of this invention. While Comparative Example 2 (without dynamic crosslinking and irradiation) outperformed Comparative Example 1, its mechanical strength, water resistance, and low-temperature toughness still showed significant differences compared to the embodiments of this invention. This demonstrates that dynamic crosslinking plays an indispensable role in constructing a stable "sea-island" structure to enhance interfacial bonding, and irradiation crosslinking plays an indispensable role in constructing a three-dimensional network to improve material durability. Comparative Example 3 (without stepwise construction) showed performance between Comparative Example 2 and the embodiments, but its water resistance and interfacial bonding were still far inferior to the embodiments of this invention. This indicates that even with dynamic crosslinking, if "water-resistant agent interfacial anchoring" and "uniform dispersion of flame retardant" cannot be achieved beforehand through a stepwise process, the functional components will still interfere with each other, failing to achieve the precise synergistic effect achieved by this invention. This fully demonstrates the unique advantages of the stepwise construction process.

[0065] In summary, through a systematic comparison of the embodiments and comparative examples, it can be clearly concluded that only by fully implementing the technical solution of the present invention (including functionalization pretreatment, stepwise construction of functional masterbatch, dynamic crosslinking, and irradiation crosslinking) can the comprehensive performance of high flame retardancy, high mechanical strength, excellent water resistance, and low-temperature toughness be simultaneously achieved; none of these can be omitted. These comparative examples powerfully demonstrate the non-obviousness and significant progressiveness of the technical solution of the present invention.

[0066] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a water-blocking cable sheath material, characterized in that, Includes the following steps: (1) Polyester-type thermoplastic polyurethane (TPU) and maleic anhydride grafts accounting for 1-3% of its mass are premixed in a high-speed mixer at 80-90°C for 5-10 minutes to obtain functionalized TPU; ethylene-vinyl acetate copolymer (EVA) and vinyltriethoxysilane accounting for 0.5-1.5% of its mass are premixed under the same conditions to obtain silane-modified EVA; (2) The nano-sized montmorillonite was calcined at 550~600℃ for 1~1.5 hours, cooled, and then dry-modified with 2~4% of its mass titanate coupling agent in a high-speed mixer at 100~110℃ for 10~15 minutes to obtain modified nano-montmorillonite; the modified nano-montmorillonite, liquid fluorocarbon resin, and nano alumina were added to an aqueous acrylic emulsion at a mass ratio of (4~5):(1.2~1.8):(1.5~2), and sheared at 50~60℃ for 15~25 minutes with a high-speed shear machine at 4000~6000 rpm to form a composite emulsion; then spray-dried to obtain a powdered functionalized nano-composite water-blocking agent; (3) Add magnesium hydroxide, microcapsule red phosphorus, nano silica, silicone powder and the silane-modified EVA obtained in step (1) into a twin-screw extruder, control the temperature at 120~140℃, melt blend and then granulate to obtain pre-dispersed flame retardant masterbatch. (4) The functionalized TPU obtained in step (1), the remaining silane-modified EVA, epoxidized soybean oil, crosslinking agent triallyl isocyanurate and zinc stearate are added to a mixer and blended at 140~150℃ and 50~70 rpm. The functionalized nanocomposite water-blocking agent obtained in step (2) is added and the mixture is continued for 2~4 minutes. When the temperature or power value of the system material reaches the peak and begins to decrease, a composite crosslinking agent composed of benzoyl peroxide and accelerator DM at a mass ratio of 1:(0.1~0.3) is added and the mixture is continued for 6~10 minutes at the same temperature to carry out the dynamic crosslinking reaction. After the reaction is completed, the material is quickly discharged, cooled and crushed to obtain the dynamic crosslinked elastomer masterbatch. (5) The dynamic cross-linked elastomer masterbatch obtained in step (4), the pre-dispersed flame retardant masterbatch obtained in step (3), polycarbonate, and lubricant EBS are fed into a twin-screw extruder. The temperature of each section is controlled within the range of 150~160℃, the screw speed is 200~300 rpm, vacuum devouring is performed, and the melt is cooled and pelletized to obtain sheath material granules. (6) The sheath material particles obtained in step (5) are irradiated by an irradiation accelerator with an irradiation dose of 5~15kGy.

2. The preparation method according to claim 1, characterized in that: In step (1), the maleic anhydride graft is a maleic anhydride-grafted polyolefin elastomer.

3. The preparation method according to claim 1, characterized in that: In step (2), the functionalized nanocomposite water-blocking agent is composed of the following components in parts by weight: 35-45 parts of modified nano montmorillonite, 10-15 parts of liquid fluorocarbon resin, 12-18 parts of nano alumina, and 30-40 parts of water-based acrylic emulsion.

4. The preparation method according to claim 1, characterized in that: In step (3), the total amount of the composite crosslinking agent added accounts for 1.0~2.0% of the total mass of functionalized TPU and silane-modified EVA.

5. The preparation method according to claim 1, characterized in that: The functionalized nanocomposite water-blocking agent prepared in step (2) accounts for 10-18% of the total mass of the sheath material; the pre-dispersed flame-retardant masterbatch prepared in step (3) accounts for 25-35% of the total mass of the sheath material.

6. A water-blocking cable sheath material, prepared by the method described in any one of claims 1 to 5, characterized in that: The raw materials, by weight, include 70-80 parts of polyester thermoplastic polyurethane, 30-40 parts of ethylene-vinyl acetate copolymer, 15-20 parts of magnesium hydroxide, 5-8 parts of microencapsulated red phosphorus, 10-15 parts of epoxidized soybean oil, 1-1.5 parts of crosslinking agent triallyl isocyanurate, 2-3 parts of zinc stearate, 3-4 parts of liquid fluorocarbon resin, 1-2 parts of lubricant EBS, 5-7 parts of polycarbonate, 8-10 parts of nano-montmorillonite, 3-5 parts of nano-alumina, 6-8 parts of water-based acrylic emulsion, 4-6 parts of silicone powder, 0.7-2.4 parts of maleic anhydride-grafted polyolefin elastomer, and 0.15-0.6 parts of vinyltriethoxysilane.

7. The water-blocking cable sheath material according to claim 6, characterized in that: The sheath material contains cross-linked polyester thermoplastic polyurethane microdomains with a size of 2~8μm formed by dynamic cross-linking, and a functionalized nanocomposite water-blocking agent anchored at the interface between the microdomain and the ethylene-vinyl acetate copolymer matrix; the sheath material as a whole has a three-dimensional cross-linked network initiated by radiation cross-linking.

8. The water-blocking cable sheath material according to claim 6 or 7, characterized in that: Its oxygen index is ≥30%, tensile strength is ≥16MPa, elongation at break is ≥300%, and water absorption after immersion in 50-meter water column pressure for 30 days is ≤8mg / cm³. 2 .

9. The water-blocking cable sheath material according to claim 8, characterized in that: The sheath material showed no surface cracking after being bent 180° around a cylinder with a diameter five times that of the cable at a low temperature of -40°C.