High-insulation heat-resistant environment-friendly cable sheath material and preparation method thereof

Abstract

The application discloses a kind of high insulation heat-resistant environment-friendly cable sheath material and preparation method thereof, belong to cable material technical field.The sheath material is by polyvinyl chloride resin 60-80 parts, modified ultrafine magnesium hydroxide 30-50 parts, epoxy fatty acid methyl ester 8-15 parts, ionic liquid modified nanosilica 3-8 parts and other raw materials, each raw material is modified or specification limited by weight parts;Its preparation method is by stage temperature control high-speed mixing after weighing, then by five temperature control zone twin-screw extruder melt extrusion, template granulation is prepared finished product.The cable sheath material prepared by the precise compatibility and modification treatment of raw materials, combined with step temperature control mixing, gradient extrusion preparation process, has excellent insulation, heat resistance and environmental protection, adapts to the use requirement of cable sheath, and the preparation process is controllable, and parameter is clear, and it is suitable for industrialized batch production.

Description

Technical Field

[0001] This invention relates to the field of cable material technology, specifically to a high-insulation, heat-resistant, and environmentally friendly cable sheath material and its preparation method. Background Technology

[0002] Cable sheaths are the core outer protective structure of cables, and their performance directly determines the cable's service life, operational safety, and environmental adaptability. As cable applications extend to high-temperature power distribution rooms, rail transit tunnels, and complex outdoor environments, the industry is placing higher demands on the insulation, heat resistance, and mechanical strength of cable sheath materials. Simultaneously, with tightening national environmental policies, traditional sheath materials containing heavy metals and non-environmentally friendly plasticizers are gradually being phased out, while low-toxicity, halogen-free, high-performance, environmentally friendly sheath materials are becoming the mainstream development trend.

[0003] Polyvinyl chloride (PVC) is the mainstream matrix resin for cable sheathing materials due to its low cost, good insulation, and excellent processability. However, pure PVC has poor heat resistance and a low heat distortion temperature, and it is prone to softening and deformation at high temperatures, leading to a decrease in insulation performance. Therefore, it needs to be modified by adding additives. Magnesium hydroxide is widely used as a halogen-free and environmentally friendly flame retardant, but it has poor compatibility with PVC and is prone to agglomeration. The silane coupling agent modification process of ultrafine magnesium hydroxide lacks precise parameter limits, resulting in inconsistent modification effects. Nano-silica can improve the strength and heat resistance of materials, but its surface is prone to agglomeration. The modification effects of existing silane and titanate coupling agents are limited, and the application research of ionic liquid modification is still in its infancy.

[0004] Regarding additive compatibility, traditional phthalic plasticizers have poor environmental performance. As an environmentally friendly alternative, the compatibility ratio of epoxy fatty acid methyl esters with PVC and their synergistic effect with other additives have not yet been optimized. PVC is prone to thermal degradation during processing and use. Although calcium-zinc composite heat stabilizers are environmentally friendly products, their effect is limited when used alone. The compounding ratio and particle size limitation with pentaerythritol polyols lack precise research, making it difficult to achieve the required heat stabilization effect.

[0005] In addition, the existing PVC-based sheath materials are mostly prepared by single-temperature mixing and conventional extrusion granulation, resulting in poor raw material dispersibility, weak interfacial bonding between additives and matrix resin, and no standardized limitations on process parameters. This leads to low product performance stability and insufficient processing controllability, making it difficult to meet the needs of industrial mass production.

[0006] In summary, current PVC-based cable sheath materials still suffer from core technical challenges: poor compatibility between the matrix and flame-retardant and reinforcing fillers, making it difficult to achieve the desired performance; a lack of precision in the design of environmentally friendly additives, resulting in insufficient synergistic effects; and the absence of standardized parameters in the manufacturing process, leading to low product performance stability and processing controllability. Therefore, developing a high-insulation, heat-resistant, and environmentally friendly cable sheath material with precise raw material compatibility, excellent additive modification effects, and standardized manufacturing processes has become an urgent technical problem to be solved in the cable materials field. Summary of the Invention

[0007] To address the aforementioned shortcomings, this invention provides a high-insulation, heat-resistant, and environmentally friendly cable sheath material and its preparation method. By precisely matching modified raw materials and using a stepwise temperature-controlled mixing gradient extrusion process, the problems of poor compatibility, insufficient heat resistance and insulation, and low process controllability of PVC sheath materials are solved.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] A high-insulation, heat-resistant, and environmentally friendly cable sheath material, by weight, is composed of the following raw materials:

[0010] 60-80 parts of polyvinyl chloride resin, 30-50 parts of modified ultrafine magnesium hydroxide, 8-15 parts of epoxy fatty acid methyl ester, 3-8 parts of ionic liquid modified nano silica, 10-20 parts of chlorinated polyethylene, 2-5 parts of composite heat stabilizer, and 0.5-2 parts of pentaerythritol stearate.

[0011] The modified ultrafine magnesium hydroxide is magnesium hydroxide that has been surface modified with silane coupling agent KH550 and has a particle size D90≤2μm.

[0012] The ionic liquid-modified nano-silica is nano-silica with a particle size of 20-50 nm, which is surface-modified using 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid.

[0013] The composite heat stabilizer is a compound of calcium-zinc composite heat stabilizer and pentaerythritol or dipentaerythritol, with a mass ratio of calcium-zinc composite heat stabilizer to pentaerythritol or dipentaerythritol of 1:0.2-0.5, and the particle size D90 of the pentaerythritol or dipentaerythritol is ≤10μm.

[0014] Preferably, the polyvinyl chloride resin is SG-3 type polyvinyl chloride resin with a viscosity of 120-140 mL / g and a volatile content of ≤0.3%.

[0015] Preferably, the modified ultrafine magnesium hydroxide is prepared by a method comprising the following steps: placing magnesium hydroxide with a particle size D90≤2μm in a 2-4% (w / w) ethanol solution of silane coupling agent KH550, refluxing and stirring at 60-80°C for 2-4 hours, filtering, and then vacuum drying at 80-100°C.

[0016] Preferably, the ionic liquid-modified nano-silica is prepared by a method comprising the following steps: dispersing nano-silica with a particle size of 20-50 nm in anhydrous ethanol, adding 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid, the amount of ionic liquid added being 5-15% of the mass of nano-silica, ultrasonically dispersing at 50-70°C for 1-3 hours, centrifuging, washing 2-4 times with anhydrous ethanol, and vacuum drying at 60-80°C.

[0017] Preferably, the epoxy fatty acid methyl ester is epoxy soybean oil methyl ester or epoxy castor oil methyl ester, with an epoxy value of 4.5-5.5%.

[0018] Preferably, the chlorinated polyethylene has a chlorine content of 35-40% and a melt flow rate of 8-12 g / 10 min at 190°C / 2.16 kg.

[0019] A method for preparing a high-insulation, heat-resistant, and environmentally friendly cable sheath material includes the following steps:

[0020] S1: Weigh each raw material according to the weight proportions, place polyvinyl chloride resin, chlorinated polyethylene, and pentaerythritol stearate in a high-speed mixer, and mix at 90-110℃ for 8-12 minutes to obtain a premix;

[0021] S2: Add modified ultrafine magnesium hydroxide, ionic liquid modified nano silica, and composite heat stabilizer to the premix, and mix at 100-120℃ for 10-15 min;

[0022] S3: Continue to add epoxy fatty acid methyl ester and mix at 110-125℃ for 5-10 minutes to obtain a mixture;

[0023] S4: The mixture is placed in a twin-screw extruder for melt extrusion at an extrusion temperature of 160-185℃ and a screw speed of 300-400 r / min. After extrusion, it is granulated to obtain cable sheath material.

[0024] Preferably, the mixing speed of the high-speed mixer in step S1 is 1000-1500 r / min.

[0025] Preferably, the twin-screw extruder in step S4 is provided with five temperature control zones along the material conveying direction, and the temperatures of each temperature control zone are set sequentially to 160-165℃, 165-170℃, 170-175℃, 175-180℃, and 180-185℃.

[0026] Preferably, in step S4, extrusion granulation is performed using a template with a template aperture of 2-4 mm.

[0027] Compared with the prior art, the present invention has the following advantages and technical effects:

[0028] This invention addresses the technical pain points of existing polyvinyl chloride cable sheath materials, such as poor compatibility of fillers, insufficient heat resistance and insulation performance, difficulty in balancing environmental protection and performance, poor dispersion effect in the preparation process, and low product performance stability. Through directional modification of functional fillers, precise formulation of raw material system, and standardized design of preparation process, the invention achieves dual optimization of sheath material performance and processing technology, with significant advantages over existing technologies, specifically reflected in four aspects.

[0029] Firstly, this invention specifically modifies the surface of functional fillers to improve the interfacial compatibility between the fillers and polyvinyl chloride (PVC) polymeric resin, solving the problems of easy agglomeration and poor dispersibility of traditional fillers. Silane coupling agent-modified ultrafine magnesium hydroxide reduces surface polarity and enhances the bonding force with the matrix; ionic liquid-modified nano-silica forms an organic modification layer, which not only solves the problem of nano-filler agglomeration but also strengthens its interfacial bonding with the matrix, allowing various fillers to be uniformly dispersed in the matrix and fully exerting their synergistic effects of flame retardancy, reinforcement, and insulation.

[0030] Secondly, this invention achieves a comprehensive improvement in insulation, heat resistance, flame retardancy, and environmental friendliness through the scientific formulation and synergistic design of the raw material system, overcoming the contradiction of difficulty in achieving all performance aspects in existing technologies. Epoxy fatty acid methyl esters are selected to replace traditional phthalic plasticizers, combining environmental friendliness with plasticizing effects; calcium-zinc composite heat stabilizers are compounded with pentaerythritol polyols, utilizing their synergistic effect to enhance the thermal stability of the matrix and inhibit thermal degradation during processing and use; chlorinated polyethylene improves the toughness and processing performance of the matrix, forming a synergistic effect with modified fillers to strengthen comprehensive mechanical properties; pentaerythritol stearate optimizes processing flowability and avoids molding defects.

[0031] Thirdly, this invention employs ionic liquid-modified nano-silica, overcoming the limitations of traditional coupling agent modification and further enhancing the insulation and heat resistance properties of the material. The ionic liquid-modified nano-silica forms a uniform insulating phase in the matrix, improving the material's volume resistivity and breakdown field strength through the nano-size effect. Simultaneously, the uniformly dispersed nano-silica forms a dense heat-resistant protective network in the matrix, enhancing the material's heat distortion temperature and thermal aging stability, thus broadening the high-temperature application scenarios for cables.

[0032] Fourth, the preparation process of this invention adopts a standardized design of stepwise temperature-controlled high-speed mixing and gradient temperature melt extrusion, solving the problems of uneven raw material dispersion, weak interfacial bonding, and low product performance stability in existing processes. Stepwise temperature-controlled mixing is designed with different temperature mixing parameters according to the characteristics of the raw materials to achieve gradual and uniform mixing of resin, filler, and additives; gradient temperature twin-screw extrusion achieves gradual melting and plasticization of materials, avoiding thermal degradation caused by local high temperature and ensuring stable product performance; standardized process parameters make the preparation process highly controllable, suitable for industrial mass production, and solve the pain points of existing process parameters lacking unified standards and large batch performance differences.

[0033] In summary, this invention represents a comprehensive innovation from raw material modification and system compatibility to the preparation process. The various technical features work synergistically to produce a sheath material with excellent overall performance and processing properties. Furthermore, the preparation process is highly controllable and the product is highly stable. This invention effectively addresses several core technical pain points of existing polyvinyl chloride cable sheath materials and can be widely used in cable sheath preparation for various scenarios such as power transmission, rail transit, and building power distribution. It has promising prospects for industry applications. Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0035] In this invention, a method for preparing a high-insulation, heat-resistant, and environmentally friendly cable sheath material includes the following steps:

[0036] S1: Weigh each raw material according to the weight proportions, place polyvinyl chloride resin, chlorinated polyethylene, and pentaerythritol stearate in a high-speed mixer, and mix at 90-110℃ for 8-12 minutes to obtain a premix;

[0037] S2: Add modified ultrafine magnesium hydroxide, ionic liquid modified nano silica, and composite heat stabilizer to the premix, and mix at 100-120℃ for 10-15 min;

[0038] S3: Continue to add epoxy fatty acid methyl ester and mix at 110-125℃ for 5-10 minutes to obtain a mixture;

[0039] S4: The mixture is placed in a twin-screw extruder for melt extrusion at an extrusion temperature of 160-185℃ and a screw speed of 300-400 r / min. After extrusion, it is granulated to obtain cable sheath material.

[0040] The working mechanism and principle of each preparation step:

[0041] The preparation method of this invention employs a stepwise temperature-controlled mixing and gradient melt extrusion process design. By precisely matching process parameters based on the structure and performance characteristics of each raw material, the polyvinyl chloride resin, modified fillers, and various additives achieve orderly fusion, interfacial bonding, and synergistic performance at different process stages. The mechanisms of action of each step and the principles of raw material synergy are as follows:

[0042] Step S1 is the premixing stage of the matrix resin and processing aids. In this stage, polyvinyl chloride resin, chlorinated polyethylene, and pentaerythritol stearate are mixed. Polyvinyl chloride resin serves as the matrix, providing basic insulation and moldability. Chlorinated polyethylene, as a modifying resin, can form a blend system with polyvinyl chloride, improving the toughness, processing flowability, and weather resistance of the matrix. Pentaerythritol stearate acts as a lubricant; its hydrophobic segments can adhere to the surface of resin particles, reducing friction between resin particles and minimizing material adhesion to equipment in subsequent processes. The process parameters in this stage are adapted to the softening characteristics of the resin, allowing the resin particles to be initially dispersed and form a uniform premix system. This lays the foundation for the subsequent addition of fillers and additives, avoiding filler agglomeration and uneven additive dispersion caused by direct mixing.

[0043] Step S2 involves the addition and mixing of modified fillers and composite heat stabilizers. Modified ultrafine magnesium hydroxide, as a halogen-free flame retardant, after modification with a silane coupling agent, allows its surface organic groups to interact with the molecular chains of polyvinyl chloride (PVC) and chlorinated polyethylene (PVC), achieving uniform dispersion of the flame retardant in the matrix. The organic modification layer on the surface of the ionic liquid-modified nano-silica forms an interfacial bond with the matrix resin. Its nano-sized particles allow it to fill the gaps between resin molecular chains, playing a reinforcing and insulating role. The calcium-zinc composite heat stabilizer in the composite heat stabilizer captures hydrogen chloride produced by the thermal degradation of PVC, while pentaerythritol polyols form stable complexes with calcium and zinc ions, enhancing the heat stabilization effect. Together, they synergistically inhibit the thermal degradation of PVC caused by temperature increases during mixing. The temperature parameters in this stage are higher than in S1, increasing the resin swelling degree and allowing the modified fillers and heat stabilizers to fully embed into the resin system, achieving a tight bond between the fillers and the matrix.

[0044] Step S3 is the mixing stage of adding epoxy fatty acid methyl ester. As an environmentally friendly plasticizer, epoxy fatty acid methyl ester's epoxy groups can interact with the polyvinyl chloride molecular chains, inserting between the molecular chains to reduce interchain forces and improve the plasticization degree and processing performance of the matrix. Simultaneously, its epoxy structure can synergistically work with the composite heat stabilizer to further enhance the thermal stability of the system. This stage involves a slight increase in temperature to allow the plasticizer to fully diffuse and become compatible with the resin system, avoiding uneven material properties caused by localized plasticizer aggregation. At the same time, the lubricating effect of pentaerythritol stearate can assist in the dispersion of the plasticizer, achieving synergistic optimization of lubrication and plasticization.

[0045] Step S4 is the melt extrusion granulation stage. The gradient temperature-controlled twin-screw extrusion process allows the material to gradually melt and plasticize from feeding to extrusion, avoiding resin thermal degradation and additive decomposition caused by localized high temperatures. The shearing action of the screw further breaks down the micro-agglomerates in the material, enabling the modified fillers and additives to achieve molecular-level dispersion in the molten resin matrix. Modified ultrafine magnesium hydroxide forms a flame-retardant network in the molten system, while ionic liquid-modified nano-silica forms an insulating and reinforcing phase. The blend of chlorinated polyethylene and polyvinyl chloride provides a stable dispersion carrier for the fillers and additives. The synergistic effect of various additives gives the molten system good flowability, thermal stability, and moldability. The template granulation process design ensures the uniformity of the finished granules and improves the convenience of subsequent processing. The precise matching of various process parameters allows the performance advantages of each raw material to be fully utilized, achieving a synergistic improvement in the material's insulation, heat resistance, flame retardancy, and processing performance, resulting in unexpected comprehensive technical effects.

[0046] To make the present invention more fully disclosed, more specific embodiments are described below.

[0047] I. Raw Material Preparation

[0048] Polyvinyl chloride resin: SG-3 type, viscosity 130mL / g, volatile content ≤0.3%;

[0049] Modified ultrafine magnesium hydroxide: particle size D90≤2μm, surface modified with silane coupling agent KH550;

[0050] Epoxidized fatty acid methyl esters: epoxidized soybean oil methyl esters, epoxy value 5.0%;

[0051] Ionic liquid-modified nano-silica: 35 nm in particle size, surface modified with 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid;

[0052] Chlorinated polyethylene: chlorine content 38%, melt flow rate 10g / 10min at 190℃ / 2.16kg;

[0053] Composite heat stabilizer: Calcium-zinc composite heat stabilizer is compounded with pentaerythritol at a mass ratio of 1:0.35, and the particle size of pentaerythritol is D90≤10μm;

[0054] Pentaerythritol stearate: Industrial grade.

[0055] II. Performance Testing Methods

[0056] Insulation performance: Volume resistivity was tested according to GB / T 1408.1, in Ω·m;

[0057] Heat resistance: Heat distortion temperature is tested according to GB / T 1633, unit: °C;

[0058] Flame retardant performance: The vertical burning grade is tested according to GB / T 2408, and it is qualified if it reaches V-0 level.

[0059] Tensile strength: Tested according to GB / T 1040.2, unit is MPa.

[0060] Elongation at break: Tested according to GB / T 1040.2, unit is %.

[0061] Thermal stability time: Tested according to GB / T 2917.1, thermal stability time at 180 °C, unit is min.

[0062] III. Examples

[0063] Example 1

[0064] 1. Preparation of modified ultrafine magnesium hydroxide: Magnesium hydroxide with particle size D90 ≤ 2 μm is placed in a 3% ethanol solution of silane coupling agent KH550, refluxed and stirred at 70 °C for 3 hours, filtered and vacuum dried at 90 °C to obtain modified ultrafine magnesium hydroxide.

[0065] 2. Preparation of ionic liquid-modified nano-silica: Nano-silica with a particle size of 35 nm is dispersed in absolute ethanol, 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid accounting for 10% of the mass of nano-silica is added, ultrasonic dispersion is carried out at 60 °C for 2 hours, centrifuged and separated, washed 3 times with absolute ethanol, and vacuum dried at 70 °C to obtain ionic liquid-modified nano-silica.

[0066] 3. Preparation of cable sheath material

[0067] S1: Weigh 70 parts of polyvinyl chloride resin, 15 parts of chlorinated polyethylene, and 1.2 parts of pentaerythritol stearate by weight, place them in a high-speed mixer, mix at a rotation speed of 1250 r / min and 100 °C for 10 min to obtain a premix.

[0068] S2: Add 40 parts of modified ultrafine magnesium hydroxide, 5.5 parts of ionic liquid-modified nano-silica, and 3.5 parts of composite heat stabilizer to the premix, and mix at 110 °C for 12 min.

[0069] S3: Continuously add 11.5 parts of epoxy fatty acid methyl ester, and mix at 118 °C for 7 min to obtain a mixed material.

[0070] S4: Place the mixed material in a twin-screw extruder. The temperatures of the five temperature control zones along the material conveying direction are 163 °C, 168 °C, 173 °C, 178 °C, and 183 °C in sequence, the screw rotation speed is 350 r / min, and pelletizing is carried out using a die (die hole diameter is 3 mm) to obtain the cable sheath material.

[0071] Single-factor experimental design and results of key process parameters

[0072] (I) Experimental Design Principles

[0073] Using Example 1 as the standard, single-factor experiments were conducted on the high-speed mixer speed, S1 stage mixing temperature, twin-screw extruder screw speed, and S2 stage mixing time, respectively. The remaining process parameters were the same as in Example 1. The three core indicators of volume resistivity, heat distortion temperature, and tensile strength were tested, and the results are as follows.

[0074] Single-factor experiment 1: Speed ​​of high-speed mixer

[0075]

[0076] Conclusion and Analysis: As shown in Table 1, when the rotation speed is below 1250 r / min, the shear force on the raw materials is insufficient, and the resin, filler and additives cannot be fully dispersed. The filler is prone to local agglomeration, resulting in weak interfacial bonding and a decrease in insulation, heat resistance and mechanical properties. When the rotation speed is above 1250 r / min, the excessive shear force will cause some resin molecular chains to break, damage the matrix structure, and the modified layer on the surface of the filler is easily destroyed, reducing the compatibility between the filler and the matrix, resulting in a slight decline in performance.

[0077] Single-factor experiment 2: Mixing temperature in stage S1

[0078]

[0079] Conclusion and Analysis: As shown in Table 2, when the temperature is below 100℃, the polyvinyl chloride resin is not sufficiently softened, chlorinated polyethylene cannot fully form a blend system with polyvinyl chloride, the lubricant cannot be uniformly adhered to the resin surface, the premix has poor dispersibility, and subsequent fillers are difficult to embed evenly. When the temperature is above 100℃, premature high temperature will cause the resin to slightly soften and clump, and pentaerythritol stearate is prone to migration and volatilization, resulting in a decrease in lubrication effect and a reduction in material performance.

[0080] Single-factor experiment 3: Screw speed of twin-screw extruder

[0081]

[0082] Conclusion and Analysis: As shown in Table 3, when the rotation speed is below 350 r / min, the shearing and plasticization of the material in the barrel is insufficient, the uniformity of the melt system is poor, the interface between the filler and the matrix is ​​not tightly bonded, and micro-voids exist, resulting in a decrease in insulation and mechanical properties. When the rotation speed is above 350 r / min, the residence time of the material in the barrel is too short, the plasticization is insufficient, and the excessive shear heat will cause a sudden rise in local temperature, which will cause slight thermal degradation of the resin, and reduce the heat distortion temperature and tensile strength.

[0083] Single-factor experiment 4: S2 stage mixing time

[0084]

[0085] Conclusion and Analysis: As shown in Table 2, when the mixing time is less than 12 minutes, the modified filler and composite heat stabilizer cannot be fully dispersed in the premix, the heat stabilizer cannot uniformly coat the resin particles, the filler agglomeration is not completely eliminated, and the insulation and heat resistance performance is limited. When the mixing time is longer than 12 minutes, the excessive mixing time will cause the system temperature to rise continuously, causing slight thermal degradation of polyvinyl chloride. At the same time, the interfacial bonding force between the filler and the matrix is ​​weakened due to excessive stirring, resulting in a slight decrease in performance.

[0086] Example 2

[0087] 1. Preparation of modified ultrafine magnesium hydroxide: Magnesium hydroxide with a particle size D90≤2μm was placed in a 2% (w / w) ethanol solution of silane coupling agent KH550, refluxed and stirred at 60℃ for 4 hours, filtered, and then vacuum dried at 80℃.

[0088] 2. Preparation of ionic liquid modified nano-silica: 20 nm nano-silica particles were dispersed in anhydrous ethanol, and 5% by weight of ionic liquid was added. The mixture was ultrasonically dispersed at 50 °C for 3 hours, centrifuged, washed twice with anhydrous ethanol, and vacuum dried at 60 °C.

[0089] 3. Preparation of cable sheath materials

[0090] S1: Weigh 60 parts of polyvinyl chloride resin, 10 parts of chlorinated polyethylene, and 0.5 parts of pentaerythritol stearate. Mix them in a high-speed mixer at 1000 r / min and 90℃ for 12 min to obtain a premix.

[0091] S2: Add 30 parts of modified ultrafine magnesium hydroxide, 3 parts of ionic liquid modified nano silica, and 2 parts of composite heat stabilizer, and mix at 100℃ for 15 min;

[0092] S3: Add 8 parts of epoxy fatty acid methyl ester, mix at 110℃ for 10 min to obtain the mixture;

[0093] S4: The twin-screw extruder has five temperature control zones with temperatures of 160℃, 165℃, 170℃, 175℃ and 180℃ respectively, a screw speed of 300r / min, and a die hole diameter of 2mm for granulation to obtain the finished product.

[0094] Example 3

[0095] 1. Preparation of modified ultrafine magnesium hydroxide: Magnesium hydroxide with a particle size D90≤2μm was placed in a 4% (w / w) ethanol solution of silane coupling agent KH550, refluxed and stirred at 80℃ for 2 hours, filtered, and then vacuum dried at 100℃.

[0096] 2. Preparation of ionic liquid modified nano-silica: 50 nm nano-silica particles were dispersed in anhydrous ethanol, and 15% by weight of ionic liquid was added. The mixture was ultrasonically dispersed at 70 °C for 1 hour, centrifuged, washed 4 times with anhydrous ethanol, and vacuum dried at 80 °C.

[0097] 3. Preparation of cable sheath materials

[0098] S1: Weigh 80 parts of polyvinyl chloride resin, 20 parts of chlorinated polyethylene, and 2 parts of pentaerythritol stearate. Mix them in a high-speed mixer at 1500 r / min and 110℃ for 8 min to obtain a premix.

[0099] S2: Add 50 parts of modified ultrafine magnesium hydroxide, 8 parts of ionic liquid modified nano silica, and 5 parts of composite heat stabilizer, and mix at 120℃ for 10 min.

[0100] S3: Add 15 parts of epoxy fatty acid methyl ester, mix at 125℃ for 5 minutes to obtain the mixture;

[0101] S4: The twin-screw extruder has five temperature control zones with temperatures of 165℃, 170℃, 175℃, 180℃, and 185℃ respectively, a screw speed of 400r / min, and a die hole diameter of 4mm for granulation to obtain the finished product.

[0102] Example 4

[0103] 1. Preparation of modified ultrafine magnesium hydroxide: Same as in Example 1.

[0104] 2. Preparation of ionic liquid-modified nano-silica: Same as in Example 1.

[0105] 3. Preparation of cable sheath materials

[0106] S1: Weigh 65 parts of polyvinyl chloride resin, 12 parts of chlorinated polyethylene, and 0.8 parts of pentaerythritol stearate. Mix them in a high-speed mixer at 1100 r / min and 95℃ for 11 min to obtain a premix.

[0107] S2: Add 35 parts of modified ultrafine magnesium hydroxide, 4 parts of ionic liquid modified nano silica, and 2.5 parts of composite heat stabilizer, and mix at 105℃ for 14 min;

[0108] S3: Add 9.5 parts of epoxy fatty acid methyl ester, mix at 113℃ for 9 minutes to obtain a mixture;

[0109] S4: The twin-screw extruder has five temperature control zones with temperatures of 162℃, 166℃, 171℃, 176℃ and 181℃ respectively, a screw speed of 320r / min, and a die hole diameter of 2.5mm for granulation to obtain the finished product.

[0110] Example 5

[0111] 1. Preparation of modified ultrafine magnesium hydroxide: Same as in Example 1.

[0112] 2. Preparation of ionic liquid-modified nano-silica: Same as in Example 1.

[0113] 3. Preparation of cable sheath materials

[0114] S1: Weigh 75 parts of polyvinyl chloride resin, 18 parts of chlorinated polyethylene, and 1.8 parts of pentaerythritol stearate. Mix them in a high-speed mixer at 1400 r / min and 105℃ for 9 min to obtain a premix.

[0115] S2: Add 45 parts of modified ultrafine magnesium hydroxide, 7 parts of ionic liquid modified nano silica, and 4.5 parts of composite heat stabilizer, and mix at 115℃ for 11 min;

[0116] S3: Add 13.5 parts of epoxy fatty acid methyl ester, mix at 122℃ for 6 minutes to obtain a mixture;

[0117] S4: The twin-screw extruder has five temperature control zones with temperatures of 164℃, 169℃, 174℃, 179℃ and 184℃ respectively, a screw speed of 380r / min, and a die hole diameter of 3.5mm for granulation to obtain the finished product.

[0118] Example 6

[0119] 1. Preparation of modified ultrafine magnesium hydroxide: Magnesium hydroxide with a particle size D90≤2μm was placed in a 2.5% (w / w) ethanol solution of silane coupling agent KH550, refluxed and stirred at 65℃ for 3.5 hours, filtered, and then vacuum dried at 85℃.

[0120] 2. Preparation of ionic liquid-modified nano-silica: 30 nm nano-silica particles were dispersed in anhydrous ethanol, and 8% by weight of ionic liquid was added. The mixture was ultrasonically dispersed at 55 °C for 2.5 hours, centrifuged, washed three times with anhydrous ethanol, and vacuum dried at 65 °C.

[0121] 3. Preparation of cable sheath materials

[0122] S1: Weigh 68 parts of polyvinyl chloride resin, 14 parts of chlorinated polyethylene, and 1.0 part of pentaerythritol stearate. Mix them in a high-speed mixer at 1200 r / min and 98℃ for 10.5 min to obtain a premix.

[0123] S2: Add 38 parts of modified ultrafine magnesium hydroxide, 5 parts of ionic liquid modified nano silica, and 3.0 parts of composite heat stabilizer, and mix at 108℃ for 13 min;

[0124] S3: Add 10.5 parts of epoxy fatty acid methyl ester and mix at 116℃ for 8 minutes to obtain a mixture.

[0125] S4: The twin-screw extruder has five temperature control zones with temperatures of 161℃, 167℃, 172℃, 177℃ and 182℃ respectively, a screw speed of 340r / min, and a die hole diameter of 2.8mm for granulation to obtain the finished product.

[0126] IV. Comparative Examples

[0127] Comparative Example 1

[0128] Unmodified ultrafine magnesium hydroxide (particle size D90≤2μm) and unmodified nano-silica (particle size 35nm) were used, and the other raw materials were the same as in Example 1;

[0129] The preparation steps and process parameters for the cable sheath material are the same as in Example 1.

[0130] Comparative Example 2

[0131] The composite heat stabilizer was replaced with a single calcium-zinc composite heat stabilizer, and the other raw materials were the same as in Example 1;

[0132] The preparation steps and process parameters for the cable sheath material are the same as in Example 1.

[0133] Comparative Example 3

[0134] The epoxy fatty acid methyl ester was replaced with diisononyl phthalate, and the other raw materials were the same as in Example 1;

[0135] The preparation steps and process parameters for the cable sheath material are the same as in Example 1.

[0136] Comparative Example 4

[0137] The raw materials are the same as in Example 1;

[0138] Preparation process: All raw materials were added to a high-speed mixer at once and mixed at 110°C for 25 minutes. The subsequent extrusion granulation parameters were the same as in Example 1.

[0139] V. Summary of Experimental Results:

[0140] (a) Test Results

[0141]

[0142] (II) Data Comparison and Analysis

[0143] 1. Insulation performance analysis

[0144] As shown in Tables 5 and 6, the volume resistivity range of Examples 1-6 is 7.2 × 10⁻⁶. 14 ~9.8×10 14 Ω·m, with Example 1 having a volume resistivity of 9.8 × 10⁻⁶ Ω·m. 14The volume resistivity of Comparative Examples 1-4 is only 9.1 × 10 Ω·m, while the highest volume resistivity is only 9.1 × 10 Ω·m. 14 In Ω·m, the volume resistivity of Example 1 was increased by 205.6% compared to Comparative Example 1, 18.1% compared to Comparative Example 2, 7.7% compared to Comparative Example 3, and 44.1% compared to Comparative Example 4.

[0145] From a theoretical perspective, this invention achieves a significant improvement in insulation performance through directional modification and uniform dispersion of fillers: an organic modification layer is formed on the surface of nano-silica modified by ionic liquid, which not only solves the problem of nano-silica agglomeration, but also forms a tight interfacial bond with the polyvinyl chloride and chlorinated polyethylene matrix, forming a continuous and uniform insulating phase in the matrix, and significantly improving the volume resistivity of the material by means of the nano-size effect; ultrafine magnesium hydroxide modified by silane coupling agent reduces surface polarity, and after being uniformly dispersed in the matrix, it forms an insulating barrier network, which synergistically constructs a dual insulating structure with the nano-silica modified by ionic liquid, further enhancing the insulation performance. In contrast, in Comparative Example 1, because the filler was not modified, the magnesium hydroxide and nano-silica had strong surface polarity, poor compatibility with the matrix, and were prone to agglomeration, forming a large number of conductive channels, resulting in a sharp drop in volume resistivity by an order of magnitude. Comparative Example 2 only lacked the composite heat stabilizer compound system, which had a small impact on insulation performance, but the uneven dispersion of the heat stabilizer still slightly reduced the matrix density, and the insulation performance was slightly lower than that of Example 1. Although the insulation performance of Comparative Example 3 was close to that of Example 1 after replacing the plasticizer, the migration of phthalic plasticizers would lead to the decay of insulation performance after long-term use. Comparative Example 4 adopted a one-time mixing process, and the filler and matrix were unevenly dispersed, with local agglomeration, which destroyed the continuity of the insulating phase and reduced the insulation performance.

[0146] 2. Heat resistance performance analysis

[0147] As shown in Tables 5 and 6, the heat distortion temperature range of Examples 1-6 is 82~89℃, with Example 1 reaching 89℃, while the highest heat distortion temperature of Comparative Examples 1-4 is only 87℃. The heat distortion temperature of Example 1 is 18.7% higher than that of Comparative Example 1, 9.9% higher than that of Comparative Example 2, 2.3% higher than that of Comparative Example 3, and 11.3% higher than that of Comparative Example 4. Regarding the thermal stability time, the thermal stability time range of Examples 1-6 is 35~42 min, with Example 1 reaching 42 min, while the highest of Comparative Examples 1-4 is only 40 min. The thermal stability time of Example 1 is 40.0% higher than that of Comparative Example 1, 50.0% higher than that of Comparative Example 2, 5.0% higher than that of Comparative Example 3, and 23.5% higher than that of Comparative Example 4.

[0148] From a theoretical perspective, this invention improves heat resistance through the synergistic effect of filler reinforcement and a thermal stabilization system: ionic liquid-modified nano-silica is uniformly dispersed in the interstices of the matrix molecular chains, forming a dense heat-resistant protective network that hinders the thermal motion of the molecular chains and increases the material's heat distortion temperature; the calcium-zinc composite heat stabilizer in the composite heat stabilizer can capture hydrogen chloride produced by the thermal degradation of polyvinyl chloride, and pentaerythritol forms a stable complex with calcium and zinc ions, delaying the thermal degradation reaction. The two work synergistically to significantly improve the material's thermal stability time; chlorinated polyethylene and polyvinyl chloride form a blend system, optimizing the thermal distortion characteristics of the matrix and further improving heat resistance. In Comparative Example 1, the unmodified filler was prone to agglomeration, failing to form a continuous heat-resistant network. Furthermore, micropores existed at the filler-matrix interface, accelerating heat conduction and causing molecular chain deformation, resulting in a significant decrease in both heat distortion temperature and heat stability time. Comparative Example 2 used a single calcium-zinc composite heat stabilizer, which could only capture hydrogen chloride but could not form a complex to stabilize the system. The thermal degradation reaction could not be effectively inhibited, leading to a significant decrease in heat stability time and a corresponding decrease in heat distortion temperature. In Comparative Example 3, after replacing the plasticizer, the heat resistance performance was close to that of Example 1, but the synergistic heat stabilizing effect of the epoxy groups of the epoxy fatty acid methyl ester and the heat stabilizer disappeared, resulting in a slightly lower heat stability time. In Comparative Example 4, the one-time mixing resulted in uneven dispersion of the heat stabilizer, with some areas lacking heat stabilizer protection, making them prone to localized thermal degradation. Simultaneously, the uneven dispersion of the filler caused defects in the heat-resistant network, leading to a decrease in heat resistance performance.

[0149] 3. Mechanical property analysis

[0150] Tensile strength

[0151] As shown in Tables 5 and 6, the tensile strength range of Examples 1-6 is 21.3~24.6 MPa, with Example 1 reaching a tensile strength of 24.6 MPa, while the highest tensile strength of Comparative Examples 1-4 is only 24.2 MPa. The tensile strength of Example 1 is 46.4% higher than that of Comparative Example 1, 9.3% higher than that of Comparative Example 2, 1.7% higher than that of Comparative Example 3, and 18.8% higher than that of Comparative Example 4.

[0152] Elongation at break

[0153] As shown in Tables 5 and 6, the elongation at break of Examples 1-6 ranged from 352% to 386%, with Example 1 achieving an elongation at break of 386%, while the highest elongation at break of Comparative Examples 1-4 was only 382%. The elongation at break of Example 1 was 33.6% higher than that of Comparative Example 1, 11.9% higher than that of Comparative Example 2, 1.0% higher than that of Comparative Example 3, and 14.2% higher than that of Comparative Example 4.

[0154] From a theoretical perspective, this invention optimizes mechanical properties through the synergistic effect of filler interface modification and matrix toughening: silane coupling agent-modified ultrafine magnesium hydroxide and ionic liquid-modified nano-silica both achieve tight interfacial bonding with the matrix. When the material is subjected to external force, the stress can be uniformly transferred to the filler through the interface, where the filler plays a reinforcing role. At the same time, the fine-grained strengthening effect of nano-silica further enhances tensile strength. Chlorinated polyethylene, as a toughening modifier, introduces flexible segments after forming a blend system with polyvinyl chloride, improving the flexibility of the matrix. Pentaerythritol stearate optimizes the processing fluidity of the material, avoiding defects such as bubbles and cracks during processing and ensuring elongation at break. The uniform dispersion of each raw material ensures uniform stress distribution within the material, avoiding the decline in mechanical properties caused by localized stress concentration. Comparative Example 1: The unmodified filler had poor compatibility with the matrix and weak interfacial bonding. Under external force, it was prone to microcracks at the interface, and the filler agglomerated to form stress concentration points, resulting in a significant decrease in tensile strength and elongation at break. Comparative Example 2: The single heat stabilizer caused slight thermal degradation of the matrix, damaging the molecular chain structure and slightly reducing mechanical properties. Comparative Example 3: After replacing the plasticizer, the mechanical properties were close to those of Example 1, but the plasticizing effect of the phthalic plasticizer was slightly inferior to that of epoxy fatty acid methyl ester, and the elongation at break decreased slightly. Comparative Example 4: One-time mixing resulted in uneven dispersion of filler and additives, stress concentration and microdefects inside the material, which easily caused crack propagation under external force, leading to a decrease in mechanical properties.

[0155] 4. Flame retardant performance analysis

[0156] As shown in Tables 5 and 6, the vertical flammability rating of Examples 1-6 all reached V-0, while Comparative Example 1 was only V-1. Although Comparative Examples 2-4 reached V-0, their flame retardant performance stability was far lower than that of Example 1.

[0157] From a theoretical perspective, this invention achieves high-efficiency flame retardancy through the uniform dispersion of modified flame-retardant fillers: ultrafine magnesium hydroxide modified with silane coupling agent is uniformly dispersed in the matrix. When heated, it decomposes and releases water of crystallization, absorbing a large amount of heat to reduce the surface temperature of the material. At the same time, the generated magnesium oxide is loose and porous, covering the material surface to form a barrier layer that isolates oxygen and heat transfer. The modified magnesium hydroxide and nano-silica work synergistically. Nano-silica can improve the density of the magnesium oxide barrier layer, further enhancing the flame retardant effect. Moreover, the uniform dispersion of the two avoids uneven flame retardant performance caused by local aggregation of flame retardants. In Comparative Example 1, the unmodified magnesium hydroxide agglomerates in the matrix. When heated, the release of water of crystallization is uneven, making it impossible to form a continuous magnesium oxide barrier layer. Furthermore, the agglomeration areas are prone to forming combustion channels, resulting in a decrease in the flame retardant rating to V-1. In Comparative Examples 2-4, due to filler modification or reasonable process design, the flame retardant can achieve a basic flame retardant effect, reaching the V-0 rating. However, the uneven dispersion of the heat stabilizer in Comparative Example 2 and the uneven dispersion of the filler in Comparative Example 4 both lead to insufficient local flame retardant concentrations. During continuous high-temperature combustion, dripping is likely to occur, resulting in insufficient stability of flame retardant performance.

[0158] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A high-insulation, heat-resistant, and environmentally friendly cable sheath material, characterized in that, By weight, it consists of the following raw materials: 60-80 parts of polyvinyl chloride resin, 30-50 parts of modified ultrafine magnesium hydroxide, 8-15 parts of epoxy fatty acid methyl ester, 3-8 parts of ionic liquid modified nano silica, 10-20 parts of chlorinated polyethylene, 2-5 parts of composite heat stabilizer, and 0.5-2 parts of pentaerythritol stearate. The modified ultrafine magnesium hydroxide is magnesium hydroxide that has been surface modified with silane coupling agent KH550 and has a particle size D90≤2μm. The ionic liquid-modified nano-silica is nano-silica with a particle size of 20-50 nm, which is surface-modified using 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid. The composite heat stabilizer is a compound of calcium-zinc composite heat stabilizer and pentaerythritol or dipentaerythritol, with a mass ratio of calcium-zinc composite heat stabilizer to pentaerythritol or dipentaerythritol of 1:0.2-0.5, and the particle size D90 of the pentaerythritol or dipentaerythritol is ≤10μm.

2. The high-insulation, heat-resistant, and environmentally friendly cable sheath material according to claim 1, characterized in that, The polyvinyl chloride resin is SG-3 type polyvinyl chloride resin with a viscosity of 120-140 mL / g and a volatile content of ≤0.3%.

3. The high-insulation, heat-resistant, and environmentally friendly cable sheath material according to claim 1, characterized in that, The modified ultrafine magnesium hydroxide is prepared by a method comprising the following steps: magnesium hydroxide with a particle size D90≤2μm is placed in an ethanol solution of silane coupling agent KH550 with a mass fraction of 2-4%, refluxed and stirred at 60-80℃ for 2-4 hours, filtered, and then vacuum dried at 80-100℃.

4. The high-insulation, heat-resistant, and environmentally friendly cable sheath material according to claim 1, characterized in that, The ionic liquid-modified nano-silica is prepared by a method comprising the following steps: dispersing nano-silica with a particle size of 20-50 nm in anhydrous ethanol, adding 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid, the amount of ionic liquid added being 5-15% of the mass of nano-silica, ultrasonically dispersing at 50-70°C for 1-3 hours, centrifuging, washing 2-4 times with anhydrous ethanol, and vacuum drying at 60-80°C.

5. The high-insulation, heat-resistant, and environmentally friendly cable sheath material according to claim 1, characterized in that, The epoxidized fatty acid methyl ester is epoxidized soybean oil methyl ester or epoxidized castor oil methyl ester, with an epoxy value of 4.5-5.5%.

6. The high-insulation, heat-resistant, and environmentally friendly cable sheath material according to claim 1, characterized in that, The chlorinated polyethylene has a chlorine content of 35-40% and a melt flow rate of 8-12 g / 10 min at 190℃ / 2.16 kg.

7. A method for preparing a high-insulation, heat-resistant, and environmentally friendly cable sheath material as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Weigh each raw material according to the weight proportions, place polyvinyl chloride resin, chlorinated polyethylene, and pentaerythritol stearate in a high-speed mixer, and mix at 90-110℃ for 8-12 minutes to obtain a premix; S2: Add modified ultrafine magnesium hydroxide, ionic liquid modified nano silica, and composite heat stabilizer to the premix, and mix at 100-120℃ for 10-15 min; S3: Continue to add epoxy fatty acid methyl ester and mix at 110-125℃ for 5-10 minutes to obtain a mixture; S4: The mixture is placed in a twin-screw extruder for melt extrusion at an extrusion temperature of 160-185℃ and a screw speed of 300-400 r / min. After extrusion, it is granulated to obtain cable sheath material.

8. The method for preparing the high-insulation, heat-resistant, and environmentally friendly cable sheath material according to claim 7, characterized in that, The mixing speed of the high-speed mixer in step S1 is 1000-1500 r / min.

9. The method for preparing the high-insulation, heat-resistant, and environmentally friendly cable sheath material according to claim 7, characterized in that, The twin-screw extruder described in step S4 is equipped with five temperature control zones along the material conveying direction, and the temperatures of each temperature control zone are set sequentially to 160-165℃, 165-170℃, 170-175℃, 175-180℃, and 180-185℃.

10. The method for preparing the high-insulation, heat-resistant, and environmentally friendly cable sheath material according to claim 7, characterized in that, In step S4, extrusion granulation is performed using a template with a template aperture of 2-4 mm.

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