Flame-retardant high-toughness cable sheath material and preparation method thereof

Abstract

The invention relates to the field of preparation of high polymer materials, in particular to a flame-retardant high-toughness cable sheath material and a preparation method thereof. According to the cable sheath material, a core-shell type inorganic flame retardant and a nano elastomer are adopted for synergistic modification, and an inorganic-organic hybrid three-dimensional network structure is formed. The sheath material comprises the following components in percentage by mass: 50% of low-density polyethylene matrix resin, 35% of a core-shell type inorganic flame retardant, 10% of a polyolefin elastomer flexibilizer, and auxiliaries such as zinc stearate, a hindered phenol antioxidant and polyethylene wax. The preparation method comprises the following steps: reacting magnesium hydroxide with a titanate coupling agent to prepare a core-shell type inorganic flame retardant; mixing the components in proportion at a high speed; and finally, carrying out melt blending through a twin-screw extruder, carrying out water-cooling, bracing and pelletizing, and drying to obtain a final product. The sheath material keeps good processability and realizes effective combination of flame retardant property and mechanical toughness at the same time.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer materials, in particular to a flame-retardant high-toughness cable sheath material and a preparation method thereof. BACKGROUND

[0002] Cables are widely used in power, communication, construction and other fields as carriers of electric energy and information transmission. Cable sheath is the outermost layer of the cable structure, which is directly exposed to the external environment. Its performance plays a decisive role in the safety, reliability and service life of the cable. The sheath material not only needs to resist the influence of environmental factors such as light, humidity, temperature change and chemical corrosion, but also needs to have excellent flame-retardant performance to prevent the flame from spreading along the cable and expanding the disaster when a fire occurs. Therefore, the development of high-performance flame-retardant cable sheath material has been an important research direction in the fields of material science and cable manufacturing. Traditional cable sheath materials are mostly based on polymers such as polyvinyl chloride (PVC) and polyethylene (PE). Among them, PVC has been widely used because of its inherent flame-retardant properties and low cost. However, PVC releases a large amount of toxic and corrosive hydrogen halide gas and smoke during combustion, which poses a serious threat to human life and safety and precision equipment. Its application is being restricted by increasingly stringent environmental and safety regulations. Polyethylene and other polyolefin materials are halogen-free, low-smoke and non-toxic, but they are flammable materials with low limiting oxygen index (LOI) and cannot meet the flame-retardant requirements. In order to give polyolefin cable materials flame-retardant properties, a large amount of flame retardant is usually added.

[0003] Among the many flame retardants, inorganic hydroxides such as aluminum hydroxide (ATH) and magnesium hydroxide (MH) are the first choice for halogen-free flame-retardant systems due to their non-toxicity, smoke suppression, environmental protection and other advantages. They play a flame-retardant role through multiple mechanisms such as heat absorption by decomposition, dilution of combustible gases and oxygen by releasing crystallization water, and residual carbon covering the substrate generated by metal oxides. However, in order to achieve effective flame-retardant grades (such as UL94 V-0), inorganic hydroxides usually require a very high addition amount (often more than 60%). Such a high filling amount will seriously deteriorate the processing flowability and mechanical properties of the polymer material, especially causing material brittleness, significant reduction in impact strength and elongation at break, making the sheath material less flexible and prone to cracking during installation and use, affecting the durability of the cable.

[0004] To overcome the negative effects of high filler loading, researchers have tried various methods. One common method is to modify the surface of inorganic flame retardants, such as using silane, titanate coupling agent treatment, aiming to improve the compatibility and interfacial bonding between the flame retardant and the polymer matrix, to some extent, to alleviate the deterioration of mechanical properties. But this method has limited effect on the extremely high filling system, and it is difficult to fundamentally solve the contradiction between toughness and flame retardancy. Another approach is to develop efficient synergistic flame retardant system, by introducing a small amount of other components (such as zinc borate, zinc stannate, carbon nanotubes, etc.) with the main flame retardant to produce synergistic effect, in order to reduce the total filler content while maintaining the flame retardant level. However, the improvement of flame retardant efficiency is still insufficient to reduce the filler content to the level that has no significant impact on toughness.

[0005] Simply adding elastomers (such as POE, EPDM) to toughen high-filled flame-retardant systems also has challenges. Elastomers can improve the toughness of the matrix, but often sacrifice the rigidity indicators such as tensile strength and modulus, and may have a negative impact on flame retardant performance (often referred to as "wax core effect"). Therefore, how to significantly improve the comprehensive mechanical properties of high-filled halogen-free flame-retardant polyolefin cable material, especially the impact toughness and flexibility, while ensuring the flame retardant performance, so that it can meet the requirements of harsh application environments, is a prominent technical problem faced by technical personnel in this field. The existing technical solutions often have difficulty in achieving an ideal balance between flame retardancy, toughness and processability. SUMMARY

[0006] Based on the above summarized problems, the present application provides a flame-retardant high-toughness cable sheath material and a preparation method thereof. The cable sheath material is modified by core-shell inorganic flame retardant and nano elastomer, and has an inorganic-organic hybrid three-dimensional network structure.

[0007] The core-shell inorganic flame retardant is prepared by reacting magnesium hydroxide with a titanate coupling agent.

[0008] Preferably, the components and contents of the cable sheath material are as follows: Base resin: 50wt% of low-density polyethylene; Core-shell inorganic flame retardant: 35wt% of magnesium hydroxide-based composite flame retardant; Toughening agent: 10wt% of polyolefin elastomer; Lubricant: 1wt% of zinc stearate; Antioxidant: 0.5wt% of hindered phenolic antioxidant; Processing aid: 3.5wt% of polyethylene wax; The polyolefin elastomer is an ethylene-octene copolymer with a melt index of 5g / 10min and a density of 0.870g / cm³.

[0009] Preferably, a preparation method of a flame-retardant high-toughness cable sheath material comprises the following specific steps: S1: Magnesium hydroxide with a particle size of 1-3 μm is pre-dried at 100°C for 2 hours, and then reacted with titanate coupling agent at 120°C for 1 hour in a high-speed mixer to form an organic coating layer on the surface of the magnesium hydroxide, thereby preparing a core-shell type inorganic flame retardant; S2: Take 100 parts of low-density polyethylene resin with a melt index of 2 g / 10 min as a reference, and add 35 parts of the core-shell type inorganic flame retardant prepared in step S1, 10 parts of polyolefin elastomer, 1 part of zinc stearate, 0.5 parts of hindered phenolic antioxidant, and 3.5 parts of polyethylene wax, and mix at high speed; S3: The mixture in step S2 is melt blended and extruded through a twin-screw extruder at 170-190°C, and then cut into particles by water cooling and drawing, thereby preparing a flame-retardant high-toughness cable sheath material.

[0010] Preferably, the mass ratio of the magnesium hydroxide to the titanate coupling agent in step S1 is 10:1.

[0011] Preferably, the high-speed mixing in step S2 is performed for 15 minutes at a mixing speed of 500 rpm.

[0012] Preferably, the core-shell type inorganic flame retardant further comprises a synergistic flame retardant accounting for 5-10% of the mass of the magnesium hydroxide, and the synergistic flame retardant is zinc stannate.

[0013] Preferably, in step S2, the high-speed mixing is performed in a segmented feeding manner: the base resin, the toughening agent, and the lubricant are first fed, and after mixing for 3 minutes, the core-shell type inorganic flame retardant, the antioxidant, and the processing aid are then fed.

[0014] Preferably, the water cooling and drawing in step S3 are performed at a cooling water temperature of 20°C and a particle length of 3 mm.

[0015] Preferably, the sheath material particles prepared in step S3 are dried by hot air at 80°C for 2 hours.

[0016] Compared with the prior art, the present application has the following beneficial effects: The flame-retardant, high-toughness cable sheath material of this invention forms an inorganic-organic hybrid three-dimensional network structure through the synergistic effect of a core-shell inorganic flame retardant and nano-elastomers, exhibiting multiple advantages in macroscopic material properties. This hybrid structure enables molecular-level bonding between the inorganic flame-retardant components and the organic polymer matrix. The flame retardant particles exist in a core-shell form, with the core being magnesium hydroxide providing flame-retardant functionality, and the shell consisting of an organic layer formed by a titanate coupling agent. This not only improves the interfacial compatibility between the flame retardant and the matrix resin but also promotes the uniform dispersion of the flame retardant in the matrix, avoiding the agglomeration phenomenon that easily occurs in traditional high-filler systems. The nano-elastomers, as toughening components, can penetrate into the hybrid network, forming physical cross-linking points with the flame retardant and the matrix. Therefore, when the material is subjected to external forces, the elastomer molecules can effectively absorb and disperse stress, preventing crack propagation. This structural design allows the core-shell flame retardant to decompose rapidly during combustion, absorbing heat and releasing water vapor. At the same time, a dense carbon layer is formed on the material surface, isolating oxygen and heat, while the elastomer network maintains the integrity of the material and prevents the formation of molten droplets, thus achieving a synergistic enhancement of flame retardancy and toughness.

[0017] Because the core-shell structure improves the dispersibility and thermal stability of the flame retardant, the sheath material exhibits excellent smoke suppression and self-extinguishing properties under flame conditions. The decomposition temperature of magnesium hydroxide matches the thermal degradation temperature of the polymer matrix, allowing it to function effectively in the early stages of a fire, slowing the combustion process. The hybrid network also promotes char formation, resulting in a more continuous and stable char layer that effectively blocks heat radiation and the diffusion of combustible gases. Compared to traditional flame retardant systems, this invention achieves a high flame retardant rating at a lower addition level (e.g., 35 wt%), reducing the negative impact of inorganic fillers on the material's mechanical properties. Simultaneously, the organic shell of the core-shell flame retardant reduces particle surface energy, improves interfacial adhesion with the polymer, and avoids a decrease in flame retardant efficiency due to interfacial defects.

[0018] The significantly improved toughness of the sheath material is primarily attributed to the synergistic toughening mechanism of nano-elastomers and hybrid networks. Elastomer particles, acting as stress concentrates, induce crazing and shear banding in the matrix, absorbing a large amount of energy. The hybrid network provides additional energy dissipation pathways, enabling the material to exhibit high ductility and tear resistance under tensile, bending, or impact loads. The sheath material shows improved elongation at break and impact strength, while exhibiting minimal decrease in stiffness, maintaining sufficient modulus to meet the mechanical protection requirements of the cable sheath. This high toughness makes the cable less prone to cracking or damage during installation and laying, extending its service life.

[0019] The sheathing material exhibits excellent melt flowability and dispersibility, attributed to the surface modification of the core-shell flame retardant reducing interparticle friction, as well as the synergistic effect of lubricants and processing aids. During extrusion, the material melt viscosity is moderate, making it less prone to charring or degradation, and the extruded surface is smooth and uniform, reducing production defects. The segmented feeding method further ensures uniform mixing of all components, avoiding processing instability caused by excessively high local concentrations. The sheathing material particles have high consistency in size and shape, facilitating subsequent processing operations, such as drying treatment to eliminate the influence of moisture and improve product stability. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for preparing a flame-retardant, high-toughness cable sheath material according to the present invention. Detailed Implementation

[0021] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0022] It should be noted that the "parts" mentioned in this invention refer to parts by weight. All raw materials are obtained through commercial channels and undergo purity testing before use to ensure that the impurity content is below 0.1%, thus avoiding any adverse effects of impurities on the mechanical properties, flame retardant properties, and processing performance of the cable sheath material. Specifically, the low-density polyethylene (LDPE) selected has a melt flow index of 2 g / 10 min (test conditions: 190℃, 2.16 kg). This melt flow index range balances the material's processing fluidity with the finished product's mechanical strength. If the melt flow index is too high, the tensile strength of the finished product will decrease; if the melt flow index is too low, it will increase the processing load on the twin-screw extruder and reduce production efficiency. The core-shell inorganic flame retardant uses magnesium hydroxide as the core and a titanate coupling agent as the shell. The magnesium hydroxide particle size is controlled between 1 and 3 μm. This particle size range allows the flame retardant to be uniformly dispersed in the matrix resin, reducing agglomeration. If the particle size is too large, the impact toughness of the material will decrease; if the particle size is too small, it will increase the preparation cost of the flame retardant and easily generate dust pollution. The synergistic flame retardant selected is nano-sized zinc stannate (500nm particle size). Nano-sized zinc stannate can synergistically interact with magnesium hydroxide to further enhance the flame retardant properties of the material, while its nano-size effect improves the material's processing fluidity. The toughening agent selected is ethylene-octene copolymer (POE) with a melt index of 5 g / 10 min (190℃, 2.16 kg) and a density of 0.870 g / cm³. This type of POE has good compatibility with LDPE and can significantly improve the material's impact toughness and elongation at break without reducing its tensile strength. The lubricant, zinc stearate, the hindered phenolic antioxidant (1010), and the processing aid, polyethylene wax (melting point 105℃), are all industrial-grade standard products to ensure the material's processing stability and long-term performance.

[0023] I. Raw Material Preparation Matrix resin: Low-density polyethylene (LDPE), model LDPE-2426H, melt index 2g / 10min (test conditions: 190℃, 2.16kg), density 0.923g / cm³, stable melt flow rate, ash content ≤0.03%, produced by Beijing Yanshan Branch of China Petroleum & Chemical Corporation, commercially available; Core-shell inorganic flame retardant raw materials: Magnesium hydroxide (Mg(OH)2): Industrial grade, purity ≥98%, particle size 1~3μm, specific surface area 10~15m² / g, whiteness ≥95%, no obvious agglomeration, produced by Qingdao Haoxin New Energy Technology Co., Ltd., commercially available. Titanium ester coupling agent: Model NDZ-101, chemical name is isopropyl tris(dioctyl pyrophosphoryloxy) titanate, active ingredient content ≥98%, density 0.98~1.02g / cm³ (25℃), refractive index 1.46~1.48 (25℃), produced by Nanjing Shuguang Chemical Group Co., Ltd., commercially available; Synergistic flame retardant: Zinc stannate (ZnSnO3), nano-sized, purity ≥99%, particle size 500nm, specific surface area 20~30m² / g, good dispersibility, produced by Shanghai Aladdin Biochemical Technology Co., Ltd., commercially available; Toughening agent: Ethylene-octene copolymer (POE), model Engage8780, melt index 5g / 10min (test conditions: 190℃, 2.16kg), density 0.870g / cm³, octene content 25%, Shore hardness D30, manufactured by Dow Chemical Company, commercially available; Lubricant: Zinc stearate (ZnSt), industrial grade, purity ≥98%, melting point 120~125℃, whiteness ≥95%, free acid content ≤0.5%, produced by Guangzhou Deli Chemical Co., Ltd., commercially available; Antioxidant: Hindered phenolic antioxidant (1010), chemical name pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid], purity ≥98%, melting point 110~125℃, ash content ≤0.1%, volatile matter ≤0.5%, produced by BASF AG, commercially available; Processing aid: Polyethylene wax (PE wax), model PE-WAX105, melting point 105℃, density 0.92~0.94g / cm³ (25℃), acid value ≤1mgKOH / g, viscosity (140℃) 80~100mPa・s, produced by Hangzhou Hemeng Chemical Co., Ltd., commercially available.

[0024] II. Performance Testing Methods Flame retardant performance: Tested according to GB / T2408-2021 "Determination of flammability of plastics - Horizontal burning method". The sample size is 125mm×13mm×3mm. The sample is placed horizontally in the combustion chamber and the free end of the sample is ignited for 30s with a specified flame (20mm high, blue flame). Then the flame is removed and the burning of the sample is observed. The burning time and burning length are recorded and the flammability rating (V-0, V-1, V-2) is evaluated. Among them, V-0 is the highest flame retardant rating. The sample is required to extinguish within 30s after the flame is removed and there should be no dripping material igniting the degreased cotton below. Impact toughness: Tested according to GB / T1843-2008 "Determination of impact strength of plastic cantilever beam", using type A notched specimens with specimen dimensions of 80mm×10mm×4mm, notch depth of 2mm, notch bottom radius of 0.25mm, test temperature of 23℃, impact velocity of 3.5m / s, 5 parallel specimens were tested for each sample, and the arithmetic mean was taken as the final notched impact strength, in kJ / m². Tensile properties: Tested according to GB / T1040.2-2006 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics". Type I specimens were used, with a total length of 170 mm, an effective length of 80 mm, a width of 10 mm, and a thickness of 4 mm. The tensile speed was 50 mm / min, and the test temperature was 23℃. Five parallel specimens were tested for each sample. The tensile strength (unit: MPa) and elongation at break (unit: %) were recorded, and the arithmetic mean was taken as the final result. Processing fluidity: Tested according to GB / T3682-2018 "Determination of melt mass flow rate (MFR) and melt volumetric flow rate (MVR) of thermoplastic plastics", the test temperature was 190℃, the loaded mass was 2.16kg, the preheating time was 5min, each sample was tested 3 times, and the arithmetic mean was taken as the final melt flow rate (MFR), the unit is g / 10min. The higher the MFR value, the better the processing fluidity of the material. Thermal stability: Tested according to GB / T2917.1-2002 "Determination of thermal stability of blends and products mainly composed of vinyl chloride homopolymers and copolymers - Part 1: Oven method". The sample size is (10±1) mm × (10±1) mm × (3±0.5) mm. The sample is placed in an oven at 150℃. The sample is taken out every 15 minutes to observe the color change. The time when the sample shows obvious discoloration (yellowing, blackening) is recorded to evaluate the thermal stability of the material. Weather resistance: Tested according to GB / T16422.2-2014 "Laboratory Light Source Exposure Test Method for Plastics Part 2: Xenon Arc Lamp", using a xenon arc lamp as the light source, with an irradiation intensity of 0.51 W / (m²・nm) (340 nm), a blackboard temperature of (65±3)℃, a relative humidity of (50±5)%, a water spray cycle of 18 min / 102 min (18 min of water spray, 102 min of no water spray), and an exposure time of 1000 h. The tensile strength and impact strength of the samples were measured before and after the test, and the tensile strength retention rate and impact strength retention rate were calculated to evaluate the weather resistance of the material. The higher the retention rate, the better the weather resistance of the material.

[0025] Example 1 See appendix Figure 1This embodiment aims to investigate the effect of core-shell inorganic flame retardants on the performance of cable sheath materials without the addition of synergistic flame retardants. The specific steps are as follows: Preparation of core-shell inorganic flame retardants: Raw material weighing: Accurately weigh 100g of magnesium hydroxide (particle size 1-3μm) and 10g of titanate coupling agent (model NDZ-101) to ensure that the mass ratio of the two is 10:1. This mass ratio has been verified by a large number of previous tests and can form a complete and uniform organic coating layer on the surface of magnesium hydroxide. If the amount of coupling agent added is too small, the coating will be incomplete and the compatibility between the flame retardant and the matrix resin will be poor. If the amount of coupling agent added is too large, the excess coupling agent will form small molecule impurities inside the material and reduce the mechanical properties of the material. Drying treatment: Place the weighed magnesium hydroxide and titanate coupling agent into a vacuum drying oven and dry for 2 hours at 100℃ and a vacuum degree of -0.08MPa. The purpose of drying is to remove moisture from the raw materials to prevent moisture from generating bubbles during the subsequent melt blending process, which would affect the density and mechanical properties of the material. If the drying temperature is too high, the titanate coupling agent will decompose prematurely; if the drying time is too short, the moisture will not be completely removed. High-speed reaction: The dried mixture is transferred to a high-speed mixer (model SHR-10A), the mixer speed is set to 800 rpm, and the temperature is raised to 120°C. The reaction is carried out at this temperature and speed for 1 hour. 120°C is the optimal temperature for the chemical reaction between the titanate coupling agent and the hydroxyl groups on the surface of magnesium hydroxide, which can promote the bonding of coupling agent molecules with the surface of magnesium hydroxide and form a stable core-shell structure. The speed of 800 rpm can ensure that the materials are fully mixed and avoid incomplete local reaction. Cooling and collection: After the reaction is complete, turn off the heating device and continue to maintain the mixer speed at 500 rpm. After the material temperature drops to room temperature (23℃), stop mixing, take out the material, and obtain core-shell magnesium hydroxide flame retardant (without synergistic flame retardant). Seal and store it to prevent moisture absorption.

[0026] Material mixing: Benchmark setting: Based on 100 parts of low-density polyethylene (LDPE), the addition amount of each component is calculated. The specific formula is as follows: 100 parts of LDPE, 10 parts of POE, 1 part of zinc stearate, 35 parts of core-shell flame retardant, 0.5 parts of antioxidant, and 3.5 parts of PE wax. Segmented feeding: A segmented feeding method is adopted. First, 100 parts LDPE, 10 parts POE, and 1 part zinc stearate are added to a high-speed mixer. The mixer speed is set to 500 rpm and mixed for 3 minutes. The matrix resin, toughening agent, and lubricant are added first, which allows the LDPE to melt fully and mix evenly with POE and zinc stearate, laying a good foundation for the subsequent addition of flame retardants and other components. Second, after the first mixing is completed, 35 parts of the core-shell flame retardant prepared above, 0.5 parts of antioxidant 1010, and 3.5 parts of PE wax are added to the mixer. The speed is maintained at 500 rpm and mixed for 12 minutes, for a total mixing time of 15 minutes. Segmented feeding avoids the problem of uneven mixing caused by adding all components at once. If the mixing time is too short, the components will be unevenly dispersed, which will lead to fluctuations in material properties. If the mixing time is too long, the material temperature will be too high, and the cross-linking reaction will occur prematurely, affecting subsequent processing. Mixing endpoint determination: During the mixing process, samples are taken every 3 minutes to observe the state of the material. When the material presents a uniform granular shape without obvious clumping or stratification, it is determined to be the mixing endpoint.

[0027] Melt blending extrusion: Equipment preparation: Select a twin-screw extruder (model TE-75, manufactured by Nanjing Keya Chemical Equipment Co., Ltd.), with a screw length-to-diameter ratio of 40:1. The barrel is divided into five parts: zone one, zone two, zone three, zone four, and the die head. Before extrusion, preheat the twin-screw extruder to ensure that the temperature of each zone reaches the set value and remains stable for 30 minutes. Temperature settings: Based on the melting temperature of LDPE and the processing characteristics of each component, the extrusion temperatures are set to 170℃ (Zone 1), 175℃ (Zone 2), 180℃ (Zone 3), 185℃ (Zone 4), and 180℃ (Die head). The lower temperature in Zone 1 prevents premature melting of the material, which could lead to blockage. The temperature gradually increases from Zone 1 to Zone 4, allowing the material to melt gradually and mix thoroughly. The die head temperature is slightly lower than that in Zone 4 to prevent excessive degradation of the material at the die head. Speed ​​setting: Set the screw speed to 300 rpm. This speed ensures that the material has sufficient residence time in the barrel (about 2 to 3 minutes) to allow the components to fully melt and blend, while avoiding excessive residence time that could lead to material degradation. If the speed is too high, the material residence time will be short and the mixing will be insufficient; if the speed is too low, the production efficiency will be low and the material will be easily degraded. Feeding and extrusion: The mixed material is evenly fed into the feed port of the twin-screw extruder through a loss-in-weight feeder (model KCM-30, manufactured by Shanghai Koperon Machinery Co., Ltd.) at a feeding rate of 50 kg / h. Under the shearing and conveying action of the screw, the material is melted, mixed and sheared in each zone and then extruded from the die head to form a continuous strip.

[0028] Post-processing: Water cooling: The extruded strip enters a water cooling tank for cooling. The water temperature in the cooling tank is set to 20℃, and the cooling length is 3m. The water temperature of 20℃ can quickly cool the strip to room temperature, preventing the strip from deforming during the cooling process. If the water temperature is too high, the cooling speed is slow and the strip is prone to sticking together; if the water temperature is too low, the strip is prone to cracking. Pelletizing process: The cooled strip is pelletized by a pelletizer (model QG-600, manufactured by Zhangjiagang Lianda Machinery Co., Ltd.). The pellet length is set to 3mm and the pelletizing speed is 500rpm. The 3mm pellet length facilitates subsequent injection molding and has good flowability. If the pellets are too long, they are easy to clog the feed port of the injection molding machine; if the pellets are too short, they are easy to generate dust. Drying process: Place the cut granules into a hot air drying oven (model 101-3, manufactured by Beijing Kewei Yongxing Instrument Co., Ltd.) and dry for 2 hours at 80℃ and a wind speed of 1.5m / s. The purpose of drying is to remove moisture from the surface of the granules to prevent moisture from forming bubbles during injection molding, which would affect the quality of the product. If the drying temperature is too high, the granules will soften and clump together; if the drying time is too short, the moisture will not be completely removed. Screening and Packaging: The dried granules are screened by a vibrating screen (model ZS-515, produced by Xinxiang Jincheng Machinery Manufacturing Co., Ltd.) with a mesh size of 10 to remove oversized or undersized granules and ensure uniform particle size. The qualified granules are then packed into sealed packaging bags and stored away from light and moisture to obtain the finished cable sheath material.

[0029] Example 2 This embodiment adds zinc stannate (5% of magnesium hydroxide by mass), a synergistic flame retardant, to Example 1 to investigate the effect of low content of synergistic flame retardant on the performance of cable sheathing materials. The specific steps are as follows: Preparation of core-shell inorganic flame retardants: Raw material weighing: Accurately weigh 100g magnesium hydroxide (particle size 1-3μm), 10g titanate coupling agent (model NDZ-101), and 5g zinc stannate (particle size 500nm), wherein zinc stannate accounts for 5% of the mass of magnesium hydroxide. This addition amount is based on the low content level determined by the previous synergistic flame retardant test, and aims to preliminarily explore the synergistic effect. Drying treatment: Place the above three raw materials in a vacuum drying oven and dry them for 2 hours at 100°C and a vacuum degree of -0.08MPa, the same as in Example 1, to ensure that the moisture in the raw materials is removed; High-speed reaction: Transfer the dried mixture into a high-speed mixer, set the speed to 800 rpm, heat to 120°C, and react for 1 hour. During the high-speed mixing process, zinc stannate will be evenly dispersed on the surface of magnesium hydroxide and form a core-shell structure together with the titanate coupling agent to enhance the flame retardant effect. Cooling and collection: After the reaction is complete, cool to room temperature, remove the material, and obtain a core-shell flame retardant containing a synergistic flame retardant. Store in a sealed container.

[0030] Material mixing: Formulation setting: Based on 100 parts LDPE, the formulation is exactly the same as that in Example 1, namely 100 parts LDPE, 10 parts POE, 1 part zinc stearate, 35 parts core-shell flame retardant, 10100.5 parts antioxidant, and 3.5 parts PE wax. This ensures that all conditions are the same except for the synergistic flame retardant, which is convenient for comparative analysis. Segmented feeding: The operation is the same as in Example 1. First, add 100 parts LDPE, 10 parts POE, and 1 part zinc stearate, and mix at 500 rpm for 3 minutes; then add 35 parts core-shell flame retardant containing synergistic flame retardant, 0.5 parts antioxidant 1010, and 3.5 parts PE wax, and continue mixing at 500 rpm for 12 minutes, for a total mixing time of 15 minutes; Mixing endpoint judgment: Same as in Example 1, observe that the material is in uniform granular form and there is no clumping or layering, then the mixing is qualified.

[0031] Melt blending extrusion: Equipment parameters: The twin-screw extruder model and screw length-to-diameter ratio are the same as in Example 1. The extrusion temperature is set to 170℃ (Zone 1), 175℃ (Zone 2), 180℃ (Zone 3), 185℃ (Zone 4), and 180℃ (die head). The screw speed is 300 rpm, and the feeding rate is 50 kg / h. This ensures that the processing conditions are exactly the same as in Example 1, eliminating the influence of processing parameters on material properties. Extrusion operation: Same as in Example 1, the mixture is fed into the twin-screw extruder through a loss-in-weight feeder, and after melting, mixing and shearing, the material is extruded from the die head as a strip.

[0032] Post-processing: Water cooling: The water temperature in the water cooling tank is 20°C, and the cooling length is 3m, consistent with Example 1; Pelletizing process: Pelletizer model, pellet length 3mm, pelletizing speed 500rpm, same as in Example 1; Drying process: The temperature of the hot air drying oven was 80℃, the drying time was 2 hours, and the wind speed was 1.5m / s, the same as in Example 1; Screening and Packaging: The material is screened with a vibrating screen to a mesh size of 10, sealed and packaged to obtain the finished cable sheath material.

[0033] Example 3 This embodiment adds zinc stannate (8% of magnesium hydroxide mass) as a synergistic flame retardant to Example 1 to investigate the effect of the medium content of the synergistic flame retardant on the performance of the cable sheath material. The specific steps are as follows: Preparation of core-shell inorganic flame retardants: Raw material weighing: Accurately weigh 100g magnesium hydroxide (particle size 1-3μm), 10g titanate coupling agent (model NDZ-101), and 8g zinc stannate (particle size 500nm). Zinc stannate accounts for 8% of the mass of magnesium hydroxide. This amount is the intermediate content that showed a good synergistic effect in the previous test. Drying treatment: Place the three raw materials into a vacuum drying oven and dry them at 100°C and a vacuum degree of -0.08MPa for 2 hours to remove moisture. The operation is the same as in Examples 1 and 2. High-speed reaction: Transfer to a high-speed mixer, rotate at 800 rpm, react at 120°C for 1 hour to ensure that zinc stannate is uniformly dispersed and participates in the formation of the core-shell structure; Cooling and Collection: Cool to room temperature, remove the core-shell flame retardant containing the synergistic flame retardant, and seal for storage.

[0034] Material mixing: Formula setting: Based on 100 parts LDPE, the formula is completely consistent with Examples 1 and 2, namely 100 parts LDPE, 10 parts POE, 1 part zinc stearate, 35 parts core-shell flame retardant, 10100.5 parts antioxidant, and 3.5 parts PE wax, ensuring that the single variable is the content of zinc stannate. Segmented feeding: First, add 100 parts LDPE, 10 parts POE, and 1 part zinc stearate, and mix at 500 rpm for 3 minutes; then add 35 parts core-shell flame retardant, 0.5 parts antioxidant 1010, and 3.5 parts PE wax, and mix at 500 rpm for 12 minutes. The total mixing time is 15 minutes. The operation process is the same as the previous two examples. End point judgment for mixing: Observe the uniformity of the material; if there is no clumping or stratification, it is considered qualified.

[0035] Melt blending extrusion: Equipment and parameters: The twin-screw extruder model and length-to-diameter ratio remain unchanged. The extrusion temperatures are 170℃ (Zone 1), 175℃ (Zone 2), 180℃ (Zone 3), 185℃ (Zone 4), and 180℃ (distillation head). The screw speed is 300 rpm, and the feeding rate is 50 kg / h, which is consistent with Examples 1 and 2. Extrusion process: The mixture is fed into the extruder via a feeder, melt-blended, and then extruded into strips, with the operation being the same as before.

[0036] Post-processing: The water cooling, pelletizing, drying, screening and packaging steps are exactly the same as those in Examples 1 and 2, namely, water cooling at 20°C, pelletizing length of 3mm, drying at 80°C for 2 hours, screening at 10 mesh and then sealing and packaging, to ensure that the post-processing conditions are consistent and to avoid additional impact on the material properties, and finally obtain the finished cable sheath material.

[0037] Example 4 This embodiment adds zinc stannate (10% of magnesium hydroxide by mass), a synergistic flame retardant, to Example 1 to investigate the effect of high content of synergistic flame retardant on the performance of cable sheathing materials. The specific steps are as follows: Preparation of core-shell inorganic flame retardants: Raw material weighing: Accurately weigh 100g magnesium hydroxide (particle size 1-3μm), 10g titanate coupling agent (model NDZ-101), and 10g zinc stannate (particle size 500nm). Zinc stannate accounts for 10% of the mass of magnesium hydroxide. This amount of addition is the maximum content of synergistic flame retardant set in this test. Drying treatment: Place the three raw materials into a vacuum drying oven and dry them at 100°C and a vacuum degree of -0.08MPa for 2 hours to remove moisture and volatile impurities from the raw materials. The operation is the same as the previous three examples. High-speed reaction: Transfer to a high-speed mixer, set the speed to 800 rpm, and heat to 120°C for 1 hour. Due to the increased amount of zinc stannate added, the material state needs to be closely observed during the mixing process to ensure uniform dispersion and avoid local agglomeration. Cooling and Collection: After the reaction is complete, cool to room temperature, remove the core-shell flame retardant containing a high content of synergistic flame retardant, seal and store it to prevent moisture absorption.

[0038] Material mixing: Formulation setting: Based on 100 parts LDPE, the formulation is exactly the same as that in Examples 1 to 3, namely 100 parts LDPE, 10 parts POE, 1 part zinc stearate, 35 parts core-shell flame retardant, 0.5 parts antioxidant, and 3.5 parts PE wax, ensuring that only the content of zinc stannate is different, so as to facilitate comparison of the influence of the content of synergistic flame retardant on performance. Segmented feeding: First, add 100 parts LDPE, 10 parts POE, and 1 part zinc stearate, and mix at 500 rpm for 3 minutes; then add 35 parts core-shell flame retardant, 0.5 parts antioxidant 1010, and 3.5 parts PE wax, and continue mixing at 500 rpm for 12 minutes, for a total mixing time of 15 minutes. The feeding sequence and mixing parameters are the same as in the previous three examples. Mixing endpoint judgment: Sampling and observing whether the material is uniform, and whether there is obvious clumping or stratification, indicates that the mixing is qualified.

[0039] Melt blending extrusion: Equipment and parameters: Twin-screw extruder model, length-to-diameter ratio 40:1, extrusion temperature 170℃ (zone 1), 175℃ (zone 2), 180℃ (zone 3), 185℃ (zone 4), 180℃ (distillation head), screw speed 300rpm, feeding rate 50kg / h, exactly the same as in Examples 1 to 3; Extrusion operation: The mixture is evenly fed into the extruder through a loss-in-weight feeder. After melting, shearing and mixing in each zone, it is extruded as a continuous strip from the die head. During the process, the appearance of the strip is observed to ensure that there are no air bubbles or impurities.

[0040] Post-processing: Water cooling: The strip enters a 20℃ water cooling tank with a cooling length of 3m to ensure rapid cooling and shaping; Pelletizing process: The cooled material strips are pelletized by a pelletizer with a pellet length of 3mm and a pelletizing speed of 500rpm to ensure uniform particle size; Drying process: Place the granules in an 80℃ hot air drying oven and dry for 2 hours at a wind speed of 1.5m / s to remove surface moisture; Screening and Packaging: A 10-mesh vibrating screen is used to screen and remove unqualified particles. Qualified particles are sealed and packaged to obtain the final cable sheath material.

[0041] Comparative Example 1 (without core-shell modification, without synergistic flame retardants) This comparative example aims to compare the impact of traditional flame retardants on the performance of cable sheath materials without core-shell modification and without synergistic flame retardants. The specific steps are as follows: Flame retardant preparation: Unmodified magnesium hydroxide is used directly as the flame retardant without titanate coupling agent coating treatment. The specifications of the unmodified magnesium hydroxide are the same as those used in Examples 1 to 4 (particle size 1 to 3 μm, purity ≥ 98%). Before use, it is also dried in a vacuum drying oven at 100°C for 2 hours to remove moisture. Material mixing: Formula setting: Based on 100 parts LDPE, the formula is as follows: 100 parts LDPE, 10 parts POE, 1 part zinc stearate, 35 parts unmodified magnesium hydroxide, 0.5 parts antioxidant, and 3.5 parts PE wax. Except for the type of flame retardant and the mixing method, the content of other components is the same as in Examples 1 to 4. One-time feeding: Unlike the segmented feeding method in Examples 1-4, this comparative example adopts a one-time feeding method, in which 100 parts of LDPE, 10 parts of POE, 1 part of zinc stearate, 35 parts of unmodified magnesium hydroxide, 0.5 parts of antioxidant 1010 and 3.5 parts of PE wax are simultaneously fed into a high-speed mixer. Mixing parameters: The mixer speed is set to 500 rpm and the mixing time is 15 minutes, which is consistent with the total mixing time of Examples 1 to 4, to ensure that the total mixing time is the same, only the feeding method is different; Judgment of mixing endpoint: After mixing for 15 minutes, take a sample to observe the state of the material. Due to the poor compatibility between unmodified magnesium hydroxide and the matrix resin, the material is prone to agglomeration. It is necessary to extend the mixing time until there are no obvious large lumps, but the total mixing time should not exceed 20 minutes to avoid overheating of the material. Melt blending extrusion: Equipment and parameters: The twin-screw extruder model and length-to-diameter ratio are the same as those in Examples 1-4. The extrusion temperature is set to 170℃ (Zone 1), 175℃ (Zone 2), 180℃ (Zone 3), 185℃ (Zone 4), and 180℃ (Die head). The screw speed is 300 rpm and the feeding rate is 50 kg / h, which is exactly the same as in Examples 1-4, to ensure consistent processing conditions. Extrusion process: Due to the poor flowability of unmodified magnesium hydroxide, the feeding rate needs to be controlled to be stable during the feeding process to avoid bridging. If bridging occurs, feeding should be stopped, the feeding port should be cleaned, and then feeding should continue. When extruding strips, due to the poor compatibility between unmodified magnesium hydroxide and the matrix resin, the strips are prone to surface roughness and unevenness. Post-processing: Water cooling: The water temperature in the water cooling tank is 20℃, and the cooling length is 3m, consistent with Examples 1 to 4; Pelletizing process: Pelletizer model, pellet length 3mm, pelletizing speed 500rpm, same as in Examples 1 to 4, but due to uneven material strips, the position of the pelletizer blades needs to be adjusted during pelletizing to ensure that the particle length deviation does not exceed ±0.5mm; Drying treatment: The granules were placed in an 80℃ hot air drying oven and dried for 2 hours at a wind speed of 1.5m / s, the same as in Examples 1 to 4; Screening and Packaging: Screening is performed using a 10-mesh vibrating screen. Due to the tendency of unmodified magnesium hydroxide to agglomerate, a large number of unqualified particles are screened out. These unqualified particles need to be collected, crushed, mixed, and extruded again. Qualified particles are sealed and packaged to obtain the finished cable sheath material.

[0042] Comparative Example 2 (without core-shell modification, containing synergistic flame retardants) This comparative example aims to compare the impact of flame retardants on the performance of cable sheath materials when no core-shell modification is performed but synergistic flame retardants are included. The specific steps are as follows: Flame retardant preparation: Raw material weighing: Accurately weigh 100g of unmodified magnesium hydroxide (particle size 1-3μm) and 10g of zinc stannate (particle size 500nm), mix them evenly, without titanate coupling agent coating treatment, and the specifications of unmodified magnesium hydroxide and zinc stannate are the same as in Examples 1-4; Premixing: Place the weighed unmodified magnesium hydroxide and zinc stannate into a high-speed mixer, set the speed to 600 rpm, and mix for 5 minutes to ensure that the two are initially mixed evenly and to avoid local concentration of zinc stannate during subsequent material mixing; Drying treatment: The mixed flame retardant was placed in a vacuum drying oven at 100°C and dried for 2 hours to remove moisture, consistent with Examples 1 to 4; Material mixing: Formulation setting: Based on 100 parts LDPE, the formulation is as follows: 100 parts LDPE, 10 parts POE, 1 part zinc stearate, 35 parts mixed flame retardant (unmodified magnesium hydroxide + zinc stannate), 0.5 parts antioxidant, and 3.5 parts PE wax. Among them, the mixed flame retardant contains 32.5 parts unmodified magnesium hydroxide and 2.5 parts zinc stannate, which is close to the relative content of zinc stannate in Example 2, so as to facilitate the comparison of the effect of core-shell modification. One-time feeding: Using a one-time feeding method, 100 parts LDPE, 10 parts POE, 1 part zinc stearate, 35 parts mixed flame retardant, 0.5 parts antioxidant 1010, and 3.5 parts PE wax are simultaneously fed into a high-speed mixer. Mixing parameters: The mixer speed was set to 500 rpm and the mixing time to 15 minutes, which is the same as the mixing parameters of Comparative Example 1. The total mixing time is the same as that of Examples 1 to 4. Judgment of mixing endpoint: Take samples every 5 minutes during the mixing process. Due to the density difference between unmodified magnesium hydroxide and zinc stannate, stratification is likely to occur. It is necessary to ensure that the mixture is mixed until there is no obvious stratification and the particles are uniform. Melt blending extrusion: Equipment and parameters: The twin-screw extruder model, length-to-diameter ratio, extrusion temperature (zone 170℃, zone 275℃, zone 380℃, zone 485℃, and die head), screw speed 300 rpm, and feeding rate 50 kg / h are consistent with those of Examples 1-4 and Comparative Example 1. Extrusion process: Since the mixed flame retardant has no core-shell modification, its compatibility with the matrix resin is still poor. The feeding rate needs to be controlled to avoid bridging. The surface of the extruded strip still has a certain roughness, but it is slightly improved compared to Comparative Example 1. Post-processing: The water cooling, pelletizing, drying, screening and packaging steps are exactly the same as those in Comparative Example 1, namely, water cooling at 20℃, pellet length of 3mm, drying at 80℃ for 2 hours, screening at 10 mesh and then sealing and packaging to ensure that the post-processing conditions are consistent, and finally the finished cable sheath material is obtained.

[0043] Comparative Example 3 (no toughening agent, core-shell modification + synergistic flame retardant) This comparative example aims to compare the impact of core-shell flame retardants on the performance of cable sheath materials without the addition of toughening agents. The specific steps are as follows: Preparation of core-shell inorganic flame retardants: The steps of weighing raw materials, drying treatment, high-speed reaction, and cooling collection are exactly the same as those in Example 4. That is, 100g of magnesium hydroxide, 10g of titanate coupling agent, and 10g of zinc stannate are weighed, dried at 100°C for 2 hours, and reacted at 120°C for 1 hour to obtain a core-shell flame retardant containing 10% zinc stannate, ensuring that the flame retardant performance is consistent with that in Example 4. Material mixing: Formula setting: Based on 100 parts LDPE, the formula is as follows: 100 parts LDPE, 1 part zinc stearate, 35 parts core-shell flame retardant, 0.5 parts antioxidant, 3.5 parts PE wax. Compared with Example 4, it lacks 10 parts POE toughening agent, while the contents of other components are the same. Segmented feeding: The segmented feeding method is similar to the feeding sequence in Examples 1-4. First, add 100 parts of LDPE and 1 part of zinc stearate, set the mixer speed to 500 rpm, and mix for 3 minutes. Second, add 35 parts of core-shell flame retardant, 0.5 parts of antioxidant 1010, and 3.5 parts of PE wax to the mixer, continue to maintain the speed of 500 rpm, and mix for 12 minutes. The total mixing time is 15 minutes. The feeding method and mixing parameters are the same as in Examples 1-4, except that the toughening agent is missing. End point judgment: Due to the lack of POE toughening agent, the flowability of the material is slightly reduced, but the mixing process still needs to ensure that the components are evenly dispersed and there is no clumping. Melt blending extrusion: Equipment and parameters: The twin-screw extruder model, length-to-diameter ratio, extrusion temperature (zone 170℃, zone 275℃, zone 380℃, zone 485℃, and die head), screw speed of 300 rpm, and feeding rate of 50 kg / h are all the same as in Examples 1 to 4. Extrusion process: Due to the lack of POE toughening agent, the melt viscosity of the material increases slightly, and the current of the extruder will be slightly higher than in Examples 1-4, but still within the normal operating range; the rigidity of the extruded strip increases and the flexibility decreases, so careful operation is required to avoid strip breakage; Post-processing: Water cooling: The water temperature in the water cooling tank is 20℃, and the cooling length is 3m, which is the same as in Examples 1 to 4. However, due to the increased rigidity of the material strip, it needs to be quickly fed into the pelletizer after cooling to avoid bending and deformation. Pelletizing process: The pelletizer model, pellet length 3mm, and pelletizing speed 500rpm are the same as in Examples 1 to 4. During the pelletizing process, the pellet strips are not easy to stick together, and the pellets have a regular appearance. Drying treatment: The granules were placed in an 80℃ hot air drying oven and dried for 2 hours at a wind speed of 1.5m / s, consistent with Examples 1 to 4; Screening and Packaging: The 10-mesh vibrating screen is used for screening. Qualified particles are sealed and packaged. Due to the lack of toughening agent, the particles have poor impact resistance. Violent collisions should be avoided during the screening process to obtain the final cable sheath material.

[0044] Formula parameter table: Note: 1. In the core-shell flame retardant, the titanate coupling agent accounts for 10% of the mass of magnesium hydroxide, and the zinc stannate accounts for 0% to 10% of the mass of magnesium hydroxide. Therefore, the actual amount of zinc stannate added in Examples 2 to 4 and Comparative Example 3 is calculated based on the total mass of the core-shell flame retardant (35 parts of core-shell flame retardant contain 31.82 parts of magnesium hydroxide + 3.18 parts of coupling agent + the corresponding proportion of zinc stannate). 2. All raw materials are of uniform specifications to ensure that, apart from the experimental variables, the characteristics of other raw materials are consistent, thus avoiding interference with the experimental results.

[0045] Performance test results table: Note: 1. The burning time is the duration of continuous burning of the sample after the flame is removed. The shorter the time, the better the flame retardant performance. 2. The dripping situation shall be judged according to GB / T2408-2021 standard. "None" means no dripping or dripping does not ignite the absorbent cotton; "Small amount" means there is a small amount of dripping but it does not ignite the absorbent cotton; "Large amount" means there is a large amount of dripping and it ignites the absorbent cotton. 3. The thermal stability time is the time it takes for the sample to show obvious discoloration in a 150℃ oven. The longer the time, the better the thermal stability. 4. Weather resistance retention rate is the ratio of the performance of the xenon arc lamp after 1000 hours of exposure to its initial performance. The higher the retention rate, the better the weather resistance.

[0046] The effect of core-shell modification on material properties: Comparing Example 1 and Comparative Example 1 (both without synergistic flame retardants), Example 1 used a core-shell flame retardant, while Comparative Example 1 used unmodified magnesium hydroxide. Performance test results show that Example 1 achieved a flame retardant rating of V-1, while Comparative Example 1 was not flame retardant. Furthermore, the notched impact strength (45.2 kJ / m²), tensile strength (12.8 MPa), elongation at break (420%), and melt flow rate (3.2 g / 10 min) of Example 1 were significantly higher than those of Comparative Example 1 (28.5 kJ / m², 10.3 MPa, 290%, and 2.1 g / 10 min, respectively). Simultaneously, the thermal stability (180 min) and weather resistance retention (85% for tensile strength and 80% for impact strength) were also superior to those of Comparative Example 1 (120 min, 65%, and 55%, respectively). This indicates that core-shell modification can improve the compatibility of magnesium hydroxide with the matrix resin, reduce agglomeration, and thus enhance the flame retardant properties, mechanical properties, processing fluidity, thermal stability, and weather resistance of the material. In the core-shell structure, the organic coating layer of the titanate coupling agent can enhance the interfacial bonding force between magnesium hydroxide and LDPE and POE, enabling stress to be uniformly transmitted within the material and improving mechanical properties; at the same time, the coating layer can reduce the surface energy of magnesium hydroxide, improve its dispersion in the matrix, and enhance flame retardant efficiency.

[0047] Comparing Example 2 and Comparative Example 2 (both containing synergistic flame retardants, without core-shell modification), Example 2 achieved a flame retardant rating of V-0, while Comparative Example 2 achieved a rating of V-1. Example 2 exhibited higher notched impact strength (48.6 kJ / m²), tensile strength (13.5 MPa), elongation at break (455%), and melt flow rate (3.5 g / 10 min) than Comparative Example 2 (32.1 kJ / m², 11.1 MPa, 330%, 2.4 g / 10 min). Its thermal stability (195 min) and weather resistance retention (88%, 83%) were also superior to Comparative Example 2 (140 min, 70%, 60%). This further demonstrates that the synergistic effect of core-shell modification and synergistic flame retardants significantly improves the overall performance of the material. Unmodified mixed flame retardants, due to poor compatibility, cannot fully exert their synergistic effect, resulting in limited performance improvement.

[0048] The effect of synergistic flame retardant content on material properties: In Examples 1-4, the content of the synergistic flame retardant zinc stannate gradually increased (0%, 5%, 8%, 10%). Performance test results showed that the flame retardant rating improved from V-1 in Example 1 to V-0 in Examples 2-4, the burning time decreased from 25 seconds to 10-12 seconds, and no dripping occurred, indicating a significant synergistic flame retardant effect between zinc stannate and magnesium hydroxide. During combustion, zinc stannate forms a dense ceramic coating covering the material surface, isolating oxygen and heat transfer, and simultaneously suppressing the dilution effect of the flame retardant caused by water vapor generated from the decomposition of magnesium hydroxide, thus improving flame retardant efficiency.

[0049] In terms of mechanical properties, as the zinc stannate content increases, the notched impact strength, tensile strength, and elongation at break first increase and then decrease. Example 3 (zinc stannate content 8%) has the best mechanical properties, with a notched impact strength of 51.3 kJ / m², a tensile strength of 14.2 MPa, and an elongation at break of 480%. The performance of Example 4 (10%) is slightly reduced. This is because an appropriate amount of nano-sized zinc stannate can play a role in heterogeneous nucleation, refine the grains, and improve mechanical properties. However, excessive addition will cause zinc stannate to agglomerate, generate stress concentration points, and reduce the mechanical properties of the material.

[0050] Regarding processing fluidity, the melt flow rate initially increased and then slightly decreased with increasing zinc stannate content, with Example 3 exhibiting the highest melt flow rate (3.7 g / 10 min). This indicates that an appropriate amount of zinc stannate can improve the processing fluidity of the material, possibly because nano-zinc stannate can reduce the internal friction of the melt. Excessive amounts, however, will increase internal friction due to agglomeration, leading to decreased fluidity. In terms of thermal stability and weather resistance, Example 3 also showed the best performance, with thermal stability at 210 min and weather resistance retention rates of 92% and 87%, respectively. This demonstrates that an appropriate amount of synergistic flame retardant can improve the long-term performance of the material, while excessive amounts will have negative effects. Overall, the material exhibits the best comprehensive performance when zinc stannate accounts for 8% of the magnesium hydroxide mass.

[0051] The effect of toughening agents on material properties: Comparing Example 4 and Comparative Example 3 (both containing core-shell flame retardant and 10% zinc stannate, Comparative Example 3 without toughening agent), the notched impact strength (49.8 kJ / m²) and elongation at break (465%) of Example 4 are significantly higher than those of Comparative Example 3 (18.7 kJ / m², 150%), while the tensile strength of Comparative Example 3 (15.6 MPa) is slightly higher than that of Example 4 (13.9 MPa). This indicates that the POE toughening agent can significantly improve the toughness and ductility of the material, while having a relatively small impact on the tensile strength. POE has good compatibility with LDPE and can form an elastic network inside the material. When the material is impacted, the elastic network can absorb the impact energy and prevent crack propagation, thereby improving impact toughness and elongation at break.

[0052] Comparative Example 3 exhibits brittle characteristics due to the lack of toughening agent. Although the flame retardant rating reaches V-0 and the processing fluidity (3.4 g / 10 min) is good, the mechanical properties cannot meet the requirements for use as cable sheath material (cable sheath needs to have a certain degree of flexibility to adapt to bending and installation). This proves that toughening agent is the key component in the preparation of high-toughness cable sheath material. The synergistic effect of core-shell flame retardant and toughening agent can improve the toughness of the material while ensuring flame retardant performance.

[0053] The effect of mixing method on material properties: Examples 1-4 used a segmented feeding method, while Comparative Examples 1-2 used a one-time feeding method. Performance test results showed that all performance indicators of Examples 1-4 were superior to those of Comparative Examples 1-2, indicating that segmented feeding allows for more uniform mixing of the components. Segmented feeding first mixes the matrix resin, toughening agent, and lubricant, allowing the LDPE to fully melt and form a uniform matrix with POE and zinc stearate. Then, flame retardants, antioxidants, and processing aids are added. This avoids interference between the flame retardant and the toughening agent / lubricant, ensuring uniform dispersion of each component in the matrix. In one-time feeding, all components are mixed simultaneously, which can lead to localized agglomeration of the flame retardant with the toughening agent and lubricant, resulting in uneven mixing and affecting material performance.

[0054] In summary, this invention, through the synergistic modification of a core-shell inorganic flame retardant (magnesium hydroxide-titanium ester coupling agent-zinc stannate) and nano-elastomer POE, and employing a segmented feeding and specific melt blending process, produces a flame-retardant high-toughness cable sheath material with excellent flame retardant properties (V-0 rating), mechanical properties (notched impact strength ≥45kJ / m², tensile strength ≥12.8MPa, elongation at break ≥420%), processing fluidity (MFR ≥3.2g / 10min), thermal stability (≥180min at 150℃), and weather resistance (performance retention ≥80% after 1000h xenon arc lamp exposure). Among these, Example 3 (zinc stannate accounting for 8% of magnesium hydroxide by mass) exhibits the best overall performance, meeting the requirements for cable use in different environments, and is particularly suitable for fields such as construction, transportation, and new energy where high flame retardancy and toughness are required.

[0055] In summary, through systematic comparison of the embodiments and comparative examples, the preparation method of the high-temperature resistant cable sheath material provided by the present invention has been fully verified. Through specific material composition, filler surface modification, and optimized processing technology (including mechanical activation, segmented temperature-controlled extrusion, pre-crystallization, segmented cross-linking, and gradient cooling), a cable sheath material with high heat resistance, excellent mechanical properties, and outstanding long-term thermal stability can be prepared, with significant technical effects.

[0056] The above embodiments demonstrate the superior effects of the present invention, while the comparative examples show a significant decrease in performance due to improper processes or proportions. The present invention is not limited to the above embodiments; any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A flame-retardant, high-toughness cable sheath material, characterized in that, The cable sheath material is synergistically modified with core-shell inorganic flame retardants and nano-elastomers, and has an inorganic-organic hybrid three-dimensional network structure. The core-shell inorganic flame retardant is prepared by reacting magnesium hydroxide with a titanate coupling agent; The cable sheath material described herein has the following components and contents: Matrix resin: 50wt% low-density polyethylene; Core-shell inorganic flame retardant: 35wt% magnesium hydroxide-based composite flame retardant; Toughening agent: 10 wt% polyolefin elastomer; Lubricant: 1 wt% zinc stearate; Antioxidant: 0.5 wt% hindered phenolic antioxidant; Processing aids: 3.5 wt% polyethylene wax; The polyolefin elastomer is an ethylene-octene copolymer with a melt index of 5 g / 10 min and a density of 0.870 g / cm³.

2. The method for preparing a flame-retardant, high-toughness cable sheath material as described in claim 1, characterized in that, The specific steps include the following: S1: Magnesium hydroxide with a particle size of 1-3 μm and titanate coupling agent are dried at 100°C for 2 hours, and then reacted at 120°C for 1 hour in a high-speed mixer to form an organic coating layer on the surface of magnesium hydroxide, thus preparing a core-shell inorganic flame retardant. S2: Take 100 parts of low-density polyethylene resin with a melt index of 2 g / 10 min as a reference, add 35 parts of the core-shell inorganic flame retardant prepared in step S1, 10 parts of polyolefin elastomer, 1 part of zinc stearate, 0.5 parts of hindered phenolic antioxidant and 3.5 parts of polyethylene wax, and mix at high speed. S3: The material mixed in step S2 is melt-blended and extruded through a twin-screw extruder at 170-190°C, and then water-cooled, drawn into strips and granulated to prepare flame-retardant high-toughness cable sheath material; In step S2, the high-speed mixing adopts a segmented feeding method: first, the matrix resin, toughening agent and lubricant are added, and after mixing for 3 minutes, the core-shell inorganic flame retardant, antioxidant and processing aid are added.

3. The method for preparing a flame-retardant, high-toughness cable sheath material as described in claim 2, characterized in that, The magnesium hydroxide and titanate coupling agent mentioned in step S1 have a mass ratio of 10:

1.

4. The method for preparing a flame-retardant, high-toughness cable sheath material as described in claim 2, characterized in that, The high-speed mixing described in step S2 lasts for 15 minutes and the mixing speed is 500 rpm.

5. The method for preparing a flame-retardant, high-toughness cable sheath material as described in claim 2, characterized in that, The core-shell inorganic flame retardant also contains a synergistic flame retardant comprising 5% to 10% of the mass of magnesium hydroxide, which is zinc stannate.

6. The method for preparing a flame-retardant, high-toughness cable sheath material as described in claim 2, characterized in that, In step S3, the water-cooled strip cutting process involves a cooling water temperature of 20°C and a cutting length of 3 mm.

7. The method for preparing a flame-retardant, high-toughness cable sheath material as described in claim 2, characterized in that, The sheath material granules obtained in step S3 are dried with hot air at 80°C for 2 hours.

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