A method for preparing a high-strength flexible cable insulation material

Abstract

The application discloses a preparation method of high-strength flexible cable insulation material and belongs to the technical field of cable insulation material preparation. The preparation method comprises the following steps: preparing a ternary compounded matrix of linear low-density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA) and ethylene-octene copolymer (POE); performing surface modification on a nano-silicon dioxide and hydroxylated multi-walled carbon nanotube composite filler by using a silane coupling agent KH550; and accurately controlling the mass ratio of a peroxide diisopropylbenzene initiator and a grafted monomer ethenyl trimethoxysilane to be 0.03-0.05, and then preparing the insulation material through melting blending, controllable grafting and warm water crosslinking. The preparation method of the high-strength flexible cable insulation material adopts a ternary compounded system of LLDPE, EVA and POE, LLDPE provides basic mechanical strength and electrical insulation, EVA improves the flexibility and adhesion of the material to the conductor, and POE significantly improves the low-temperature impact resistance and bending resistance of the material, and the three components synergistically make the material have high strength and high flexibility.

Description

Technical Field

[0001] This invention belongs to the field of cable insulation material preparation technology, specifically relating to a method for preparing a high-strength flexible cable insulation material. Background Technology

[0002] Cable insulation materials are core components that ensure the safety of power transmission and the service life of cables. With the rapid development of industrial automation, new energy vehicles and intelligent equipment industries, the application scenarios of flexible cables are becoming increasingly widespread, which puts forward higher requirements for insulation materials: they must not only have excellent electrical insulation performance, but also meet comprehensive performance requirements such as high strength, high flexibility, low temperature bending resistance and aging resistance.

[0003] In existing technologies, polyethylene (PE) is the most widely used cable insulation matrix material due to its excellent electrical insulation, processability, and chemical corrosion resistance. However, pure polyethylene has defects such as low mechanical strength, poor heat resistance, and easy brittleness at low temperatures, which cannot meet the requirements of high-strength flexible cables. To improve its performance, the industry usually uses methods such as adding inorganic fillers and chemical cross-linking for modification. In terms of inorganic filler modification, fillers such as nano-silica, calcium carbonate, and talc are commonly used to improve the material strength. However, nano-fillers have high surface energy and are prone to agglomeration. Moreover, they have poor interfacial compatibility with the non-polar polyethylene matrix, resulting in uneven filler dispersion. This can actually reduce the elongation at break and flexibility of the material, leading to the contradiction of "increased strength but decreased flexibility". Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a high-strength flexible cable insulation material to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a high-strength flexible cable insulation material, comprising the following steps: S1. Dry 50-70 parts by weight of linear low-density polyethylene, 20-30 parts by weight of ethylene-vinyl acetate copolymer and 10-20 parts by weight of ethylene-octene copolymer at 800℃-90℃ and vacuum degree of -0.08 to -0.09MPa for 4-6 hours. S2. Preheat 3-8 parts of nano-silica and 1-3 parts of hydroxylated multi-walled carbon nanotubes at 100℃-120℃ for 10min-15min, add 0.5-1.5 parts of silane coupling agent KH550, and mix at high speed using a high-speed mixer for 20min-30min to obtain surface-modified composite filler. S3. Add the pretreated matrix resin to a twin-screw extruder and melt-plasticize at 140℃-160℃ for 3-5 minutes. Add surface-modified composite filler, 0.2-0.5 parts of antioxidant 1010, 0.1-0.3 parts of antioxidant 168 and 0.5-1.0 parts of ultraviolet absorber UV-327, and blend at 200-300 r / min for 10-15 minutes. S4. Add 1.5-3.0 parts of vinyltrimethoxysilane and 0.05-0.15 parts of dicumyl peroxide, and perform a grafting reaction at 160℃-170℃ for 5 min-8 min to obtain a grafted blend. S5. Extrude the grafted blend at 150℃-165℃, cool it with water, and pelletize it to obtain grafted masterbatch. S6. After drying the grafted masterbatch, it is extruded and coated onto the surface of the cable conductor at 140℃-155℃, and then crosslinked in warm water at 80℃-90℃ for 12-24 hours to obtain a high-strength flexible cable insulation material.

[0006] In a preferred embodiment, the linear low-density polyethylene in step S1 has a melt index of 1-3 g / 10 min, the vinyl acetate content in the ethylene-vinyl acetate copolymer is 18%-28% by mass, and the octene content in the ethylene-octene copolymer is 20%-30% by mass.

[0007] In a preferred embodiment, the average particle size of the nano-silica in step S2 is 15nm-30nm, the outer diameter of the hydroxylated multi-walled carbon nanotubes is 8nm-15nm, the length is 10μm-30μm, and the hydroxyl content is 2wt%-4wt%.

[0008] In a preferred embodiment, the speed of the high-speed mixer in step S2 is 2000 r / min-3000 r / min, and the silane coupling agent KH550 is added by dropping for 5 min-10 min.

[0009] In a preferred embodiment, the temperatures of each zone of the twin-screw extruder in step S3 are as follows: Zone 1 140℃-145℃, Zone 2 145℃-150℃, Zone 3 150℃-155℃, Zone 4 155℃-160℃, and Die head 155℃-160℃.

[0010] In a preferred embodiment, the mass ratio of the initiator dicumyl peroxide to vinyltrimethoxysilane in step S4 satisfies the following formula:

[0011] In the formula: For the mass of dicumyl peroxide, The mass of vinyltrimethoxysilane.

[0012] In a preferred embodiment, the rotation speed of the pelletizer in step S5 is 300 r / min-500 r / min, and the particle size of the obtained grafted masterbatch is 2 mm-4 mm.

[0013] In a preferred embodiment, in step S6, the grafted masterbatch is vacuum dried at 90℃-100℃ for 2h-3h, the screw speed of the cable extruder is 60r / min-100r / min, and the thickness of the extruded insulation layer is 0.5mm-2.0mm.

[0014] In a preferred embodiment, during the warm water crosslinking process in step S6, the conductivity of water is less than 10 μS / cm.

[0015] In a preferred embodiment, after the warm water crosslinking is completed in step S6, the insulating material is dried with hot air at 60℃-70℃ for 4h-6h.

[0016] Compared with the prior art, the beneficial effects of the present invention are: In this invention, a ternary composite system of LLDPE, EVA and POE is adopted. LLDPE provides basic mechanical strength and electrical insulation, EVA improves the material's flexibility and adhesion to conductors, and POE significantly improves the material's low-temperature impact resistance and bending resistance. The synergistic effect of the three enables the material to have both high strength and high flexibility.

[0017] In this invention, nano-silica and hydroxylated multi-walled carbon nanotubes are combined as reinforcing fillers. Nano-silica improves the tensile strength and heat resistance of the material, while a small amount of hydroxylated multi-walled carbon nanotubes form a micro-network structure below the percolation threshold, further enhancing mechanical properties without affecting electrical insulation. The composite filler is surface modified by silane coupling agent KH550, which introduces amino active groups on the filler surface, forming chemical bonds with the matrix resin, significantly improving interfacial bonding and avoiding performance degradation caused by filler agglomeration.

[0018] In this invention, by precisely controlling the mass ratio of initiator DCP to graft monomer VTMS within the range of 0.03-0.05, the grafting rate is controlled at the optimal level, which ensures sufficient crosslinking degree to improve the strength and heat resistance of the material, while avoiding the material becoming brittle due to excessive crosslinking. The warm water crosslinking process is adopted, which is gentle and uniform, with no small molecule residue, and is environmentally friendly and low in cost. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments.

[0021] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0022] Please see Figure 1 This invention provides a method for preparing a high-strength flexible cable insulation material, comprising the following steps: Step S1: 50-70 parts by weight of linear low-density polyethylene (LLDPE), 20-30 parts by weight of ethylene-vinyl acetate copolymer (EVA), and 10-20 parts by weight of ethylene-octene copolymer (POE) are dried at 80-90℃ and a vacuum of -0.08 to -0.09 MPa for 4-6 hours to remove adsorbed and bound water from the raw materials. This prevents defects such as bubbles and pinholes caused by moisture vaporization during processing, thus ensuring uniform and stable electrical insulation and mechanical properties of the material. This step uses vacuum drying instead of ordinary hot air drying, which can achieve efficient dehydration at a lower temperature and prevent the resin from undergoing oxidative degradation due to prolonged high temperatures.

[0023] Step S2: Preheat 3-8 parts of nano-silica and 1-3 parts of hydroxylated multi-walled carbon nanotubes at 100-120℃ for 10-15 minutes to remove adsorbed moisture on the filler surface and activate the surface hydroxyl groups. Then add 0.5-1.5 parts of silane coupling agent KH550 and mix at high speed for 20-30 minutes to obtain the surface-modified composite filler. This step uses a dry surface modification process, which does not require the use of organic solvents, making it environmentally friendly and low-cost. The preheating treatment allows for a more complete reaction between the coupling agent and the hydroxyl groups on the filler surface, improving the modification effect.

[0024] Step S3: Add the pretreated matrix resin to a twin-screw extruder and melt-plasticize at 140-160℃ for 3-5 minutes to ensure complete melting and a uniform melt. Then add surface-modified composite filler, 0.2-0.5 parts of antioxidant 1010, 0.1-0.3 parts of antioxidant 168, and 0.5-1.0 parts of UV absorber UV-327. Blend at 200-300 rpm for 10-15 minutes to ensure thorough dispersion and mixing of all components under shear force. This step uses a step-by-step feeding method, first melting and plasticizing the matrix resin before adding the filler and additives. This effectively prevents filler agglomeration and improves dispersion uniformity. The combination of antioxidant 1010 and antioxidant 168 forms a synergistic antioxidant system, significantly improving the material's thermo-oxidative aging performance. UV absorber UV-327 absorbs ultraviolet light, preventing photoaging during outdoor use.

[0025] Step S4: Add 1.5-3.0 parts of vinyltrimethoxysilane (VTMS) and 0.05-0.15 parts of dicumyl peroxide (DCP) to the fourth zone of the twin-screw extruder, and carry out the grafting reaction at 160-170℃ for 5-8 minutes to obtain the grafted blend. This step adopts a reactive extrusion grafting process, integrating the grafting reaction and melt blending process into a twin-screw extruder, resulting in high production efficiency and good grafting uniformity. By precisely controlling the reaction temperature and time, the initiator decomposition rate is matched with the grafting reaction rate, avoiding premature decomposition that would lead to a low grafting rate.

[0026] Step S5: The grafted blend is extruded through a twin-screw extruder at 150-165℃, cooled to below 40℃ by circulating water at 20-25℃, and then pelletized to obtain grafted masterbatch with uniform particle size. This step uses low-temperature water cooling to rapidly cool the melt, preventing pre-crosslinking of the grafted masterbatch at high temperatures and ensuring its subsequent processing performance.

[0027] Step S6: After vacuum drying the grafted masterbatch at 90-100℃ for 2-3 hours, add it to a cable extruder and extrude it at 140-155℃ to coat the surface of the cable conductor. Then, perform warm water crosslinking in deionized water at 80-90℃ for 12-24 hours. After crosslinking, dry it with hot air at 60-70℃ for 4-6 hours to obtain the high-strength flexible cable insulation material. This step uses a warm water crosslinking process, which is gentle and uniform, and the degree of crosslinking can be precisely controlled by the crosslinking time. Using deionized water for crosslinking avoids the adsorption of impurity ions on the surface or inside the insulation layer, ensuring the electrical insulation performance of the material.

[0028] The linear low-density polyethylene (LLDPE) described in step S1 has a melt index of 1-3 g / 10 min (test conditions: 190℃, 2.16 kg). LLDPE within this melt index range exhibits both good mechanical strength and processing fluidity. The vinyl acetate content in the ethylene-vinyl acetate copolymer is 18-28% by mass. If the vinyl acetate content is too low, the improvement in flexibility will be insignificant, while if it is too high, it will reduce the mechanical strength and heat resistance of the material. The octene content in the ethylene-octene copolymer is 20-30% by mass. POE within this content range has the best compatibility with the polyethylene matrix and the best toughening effect.

[0029] The average particle size of the nano-silica in step S2 is 15-30 nm. If the particle size is too small, the surface energy will be too high and it will be more prone to agglomeration. If the particle size is too large, the reinforcing effect will not be obvious. The outer diameter of the hydroxylated multi-walled carbon nanotube is 8-15 nm, the length is 10-30 μm, and the hydroxyl content is 2-4 wt%. The aspect ratio of carbon nanotubes of this specification is moderate, which can form an effective micro-network reinforcement structure without causing processing difficulties due to excessive aspect ratio. The surface hydroxyl content ensures the reactivity with silane coupling agent.

[0030] In step S2, the high-speed mixer rotates at 2000-3000 r / min. The shear force and friction generated at this speed can fully disperse the filler and make the coupling agent uniformly coat the surface of the filler. The silane coupling agent KH550 is added by dropping over a period of 5-10 minutes to avoid excessive local concentration and self-polymerization reaction caused by adding it all at once.

[0031] The temperatures of each zone of the twin-screw extruder in step S3 are as follows: Zone 1 140-145℃, Zone 2 145-150℃, Zone 3 150-155℃, Zone 4 155-160℃, and the die head 155-160℃. A gradient heating method is used to gradually melt and plasticize the resin, avoiding resin degradation due to sudden temperature increases; Zone 4 is set to the highest temperature to provide suitable temperature conditions for the subsequent grafting reaction.

[0032] The mass ratio of the initiator dicumyl peroxide to vinyltrimethoxysilane in step S4 satisfies the following formula:

[0033] In the formula: For the mass of dicumyl peroxide, The mass of vinyltrimethoxysilane.

[0034] The mass ratio range is one of the key technical parameters of this invention. When the mass ratio is less than 0.03, the number of free radicals generated by the initiator is insufficient, the grafting rate is low, the degree of crosslinking is insufficient, and the mechanical strength and heat resistance of the material are poor. When the mass ratio is greater than 0.05, the free radicals generated by the initiator are too many, which can easily lead to the breakage of the resin molecular chain and crosslinking side reactions, making the material brittle and significantly reducing its flexibility and low-temperature performance.

[0035] In step S5, the pelletizer rotates at 300-500 r / min, resulting in grafted masterbatch with a particle size of 2-4 mm. Masterbatch within this particle size range exhibits good flowability and uniform feeding, facilitating subsequent cable extrusion processing.

[0036] In step six, the screw speed of the cable extruder is 60-100 r / min, and the thickness of the extruded insulation layer is 0.5-2.0 mm. By controlling the screw speed and extrusion temperature, the thickness and surface quality of the insulation layer can be precisely controlled, ensuring the electrical and mechanical properties of the cable.

[0037] In step S6, during the warm water crosslinking process, the conductivity of water is less than 10 μS / cm, which prevents impurity ions in the water from migrating into the interior of the insulating layer during the crosslinking process, thereby reducing the volume resistivity and breakdown strength of the material.

[0038] Example 1

[0039] A method for preparing a high-strength flexible cable insulation material includes the following steps: S1. 60 parts by weight of linear low-density polyethylene (melt index 2 g / 10 min), 25 parts by weight of ethylene-vinyl acetate copolymer (vinyl acetate content 23%) and 15 parts by weight of ethylene-octene copolymer (octene content 25%) were dried at 85°C and vacuum degree -0.085 MPa for 5 hours. S2. Add 5 parts of nano-silica (average particle size 20nm) and 2 parts of hydroxylated multi-walled carbon nanotubes (outer diameter 10nm, length 20μm, hydroxyl content 3wt%) to a high-speed mixer, preheat at 110℃ for 12 minutes, add 1.0 part of silane coupling agent KH550 by dropping over 8 minutes, and continue high-speed mixing at 2500r / min for 25 minutes to obtain surface-modified composite filler. S3. Add the pretreated matrix resin to a twin-screw extruder. Set the temperature of each zone of the twin screw extruder as follows: Zone 1 142℃, Zone 2 148℃, Zone 3 152℃, Zone 4 158℃, and the die head 158℃. Melt and plasticize at 150℃ for 4 minutes. Add surface-modified composite filler, 0.3 parts antioxidant 1010, 0.2 parts antioxidant 168, and 0.7 parts ultraviolet absorber UV-327. Blend at 250r / min for 12 minutes. S4. Add 2.2 parts of vinyltrimethoxysilane and 0.088 parts of dicumyl peroxide (mass ratio m(DCP) / m(VTMS)=0.04) to a twin-screw extruder, and carry out the grafting reaction at 165°C for 6 minutes to obtain the grafted blend. S5. Extrude the grafted blend at 160°C, cool it with water, and then pelletize it with a pelletizer at 400 r / min to obtain grafted masterbatch with a particle size of about 3 mm. S6. The grafted masterbatch is vacuum dried at 95°C for 2.5 hours, added to a cable extruder, and extruded at 150°C to coat the surface of the copper conductor. The screw speed is 80 r / min and the insulation layer thickness is 1.0 mm. Then, it is crosslinked in warm water at 85°C with a conductivity of 5 μS / cm for 18 hours. After crosslinking, it is dried with hot air at 65°C for 5 hours to obtain the high-strength flexible cable insulation material.

[0040] Example 2

[0041] A method for preparing a high-strength flexible cable insulation material includes the following steps: S1. 50 parts by weight of linear low-density polyethylene (melt index 1 g / 10 min), 30 parts by weight of ethylene-vinyl acetate copolymer (vinyl acetate content 18%) and 20 parts by weight of ethylene-octene copolymer (octene content 20%) were dried at 80 °C and vacuum degree -0.09 MPa for 6 hours. S2. Add 3 parts of nano-silica (average particle size 15nm) and 1 part of hydroxylated multi-walled carbon nanotubes (outer diameter 8nm, length 10μm, hydroxyl content 2wt%) to a high-speed mixer, preheat at 100℃ for 15 minutes, add 0.5 parts of silane coupling agent KH550 by dropping over 5 minutes, and continue high-speed mixing at 2000r / min for 30 minutes to obtain surface-modified composite filler. S3. Add the pretreated matrix resin to a twin-screw extruder. Set the temperature of each zone of the twin screw extruder as follows: Zone 1 140℃, Zone 2 145℃, Zone 3 150℃, Zone 4 155℃, and the die head 155℃. Melt and plasticize at 140℃ for 5 minutes. Add surface-modified composite filler, 0.2 parts of antioxidant 1010, 0.1 parts of antioxidant 168, and 0.5 parts of ultraviolet absorber UV-327. Blend at 200r / min for 15 minutes. S4. Add 1.5 parts of vinyltrimethoxysilane and 0.045 parts of dicumyl peroxide (mass ratio m(DCP) / m(VTMS)=0.03) to a twin-screw extruder and carry out the grafting reaction at 160℃ for 8 minutes to obtain a grafted blend; Step 5. Extrude the grafted blend at 150℃, cool it with water, and then pelletize it with a pelletizer at a speed of 300r / min to obtain grafted masterbatch with a particle size of about 2mm; S6. The grafted masterbatch is vacuum dried at 90°C for 3 hours, added to a cable extruder, and extruded at 140°C to coat the surface of the copper conductor. The screw speed is 60 r / min and the insulation layer thickness is 0.5 mm. Then, it is crosslinked in warm water at 80°C with a conductivity of 8 μS / cm for 24 hours. After crosslinking, it is dried with hot air at 60°C for 6 hours to obtain the high-strength flexible cable insulation material.

[0042] Example 3

[0043] A method for preparing a high-strength flexible cable insulation material includes the following steps: S1. 70 parts by weight of linear low-density polyethylene (melt index 3 g / 10 min), 20 parts by weight of ethylene-vinyl acetate copolymer (vinyl acetate content 28%) and 10 parts by weight of ethylene-octene copolymer (octene content 30%) were dried at 90 °C and vacuum degree -0.08 MPa for 4 hours. S2. Add 8 parts of nano-silica (average particle size 30nm) and 3 parts of hydroxylated multi-walled carbon nanotubes (outer diameter 15nm, length 30μm, hydroxyl content 4wt%) to a high-speed mixer, preheat at 120℃ for 10 minutes, add 1.5 parts of silane coupling agent KH550 dropwise over 10 minutes, and continue high-speed mixing at 3000r / min for 20 minutes to obtain the surface-modified composite filler. S3. Add the pretreated matrix resin to a twin-screw extruder. Set the temperature of each zone of the twin screw extruder as follows: Zone 1 145℃, Zone 2 150℃, Zone 3 155℃, Zone 4 160℃, and the die head 160℃. Melt and plasticize at 160℃ for 3 minutes. Add surface-modified composite filler, 0.5 parts antioxidant 1010, 0.3 parts antioxidant 168, and 1.0 part ultraviolet absorber UV-327. Blend at 300r / min for 10 minutes. S4. Add 3.0 parts of vinyltrimethoxysilane and 0.15 parts of dicumyl peroxide (mass ratio m(DCP) / m(VTMS)=0.05) to a twin-screw extruder and carry out the grafting reaction at 170℃ for 5 minutes to obtain a grafted blend; Step 5. Extrude the grafted blend at 165℃, cool it with water, and then pelletize it with a pelletizer at a speed of 500r / min to obtain grafted masterbatch with a particle size of about 4mm; S6. The grafted masterbatch is vacuum dried at 100°C for 2 hours, added to a cable extruder, and extruded at 155°C to coat the surface of the copper conductor. The screw speed is 100 r / min and the insulation layer thickness is 2.0 mm. Then, it is crosslinked in warm water at 90°C with a conductivity of 3 μS / cm for 12 hours. After crosslinking, it is dried with hot air at 70°C for 4 hours to obtain the high-strength flexible cable insulation material.

[0044] Comparative Example 1 The difference from Example 1 is that only 60 parts of linear low-density polyethylene are used as the matrix resin, and no EVA and POE are added. The remaining steps and parameters are the same as in Example 1.

[0045] Comparative Example 2 The difference from Example 1 is that hydroxylated multi-walled carbon nanotubes are not added in step S2, and only 7 parts of nano-silica are used as filler. The remaining steps and parameters are the same as in Example 1.

[0046] Comparative Example 3 The difference from Example 1 is that the composite filler in step S2 is not surface modified and is directly added to the twin-screw extruder to be blended with the matrix resin. The remaining steps and parameters are the same as in Example 1.

[0047] Comparative Example 4 The difference from Example 1 is that the amount of dicumyl peroxide used in step S4 is 0.033 parts, i.e., m(DCP) / m(VTMS)=0.015, which is lower than the range defined by the present invention. The remaining steps and parameters are the same as those in Example 1.

[0048] Comparative Example 5 The difference from Example 1 is that the amount of dicumyl peroxide used in step S4 is 0.176 parts, i.e., m(DCP) / m(VTMS)=0.08, which is higher than the range defined by the present invention. The remaining steps and parameters are the same as those in Example 1.

[0049] Performance testing The cable insulation materials prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance tests according to the following standards: Tensile strength and elongation at break: Tested according to GB / T1040.2-2006 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics", with a tensile rate of 50 mm / min; Volume resistivity: Tested according to GB / T1410-2006 "Test methods for volume resistivity and surface resistivity of solid insulating materials", test temperature 23℃; Breakdown strength: Tested according to GB / T1408.1-2006 "Electrical strength test methods for insulating materials - Part 1: Tests at power frequency", using ball-plate electrodes, with a voltage ramp rate of 1kV / s; Low-temperature bending performance: Tested according to GB / T2951.14-2008 "General test methods for insulation and sheath materials of cables and optical fibers - Part 14: General test methods - Low temperature test", with a test temperature of -40℃ and a bending radius of 5 times the insulation thickness. Record the number of bends when cracks appear.

[0050] Example 1 23.5 580 <![CDATA[2.3×10¹ 5 ]]> 36.2 >1500 Example 2 21.2 620 <![CDATA[2.7×10¹ 5 ]]> 34.8 >1500 Example 3 25.1 520 <![CDATA[1.8×10¹ 5 ]]> 37.5 1200 Comparative Example 1 16.8 350 <![CDATA[3.1×10¹ 5 ]]> 32.1 280 Comparative Example 2 19.3 460 <![CDATA[2.5×10¹ 5 ]]> 33.7 650 Comparative Example 3 17.6 380 <![CDATA[1.2×10¹ 5 ]]> 28.5 420 Comparative Example 4 18.5 550 <![CDATA[2.1×10¹ 5 ]]> 31.3 890 Comparative Example 5 24.2 320 <![CDATA[2.4×10¹ 5 ]]> 35.6 350 In this invention, a ternary composite system of LLDPE, EVA and POE is used. LLDPE provides basic mechanical strength and electrical insulation, EVA improves the material's flexibility and adhesion to conductors, and POE significantly improves the material's low-temperature impact resistance and bending resistance. The synergistic effect of the three components enables the material to have both high strength and high flexibility.

[0051] Surface modification of composite fillers solves agglomeration problems and enhances interfacial bonding: Nano-silica and hydroxylated multi-walled carbon nanotubes are used as reinforcing fillers. Nano-silica improves the tensile strength and heat resistance of the material, while a small amount of hydroxylated multi-walled carbon nanotubes form a micro-network structure below the percolation threshold, further enhancing mechanical properties without affecting electrical insulation. The surface of the composite filler is modified by silane coupling agent KH550, which introduces amino active groups on the filler surface, forming chemical bonds with the matrix resin, significantly improving interfacial bonding and avoiding performance degradation caused by filler agglomeration.

[0052] Controlled silane grafting crosslinking optimizes the overall performance of materials: By precisely controlling the mass ratio of initiator DCP to graft monomer VTMS within the range of 0.03-0.05, the grafting rate is controlled at the optimal level, ensuring sufficient crosslinking degree to improve the strength and heat resistance of the material, while avoiding the brittleness caused by excessive crosslinking; the warm water crosslinking process is adopted, which is gentle and uniform, leaves no small molecule residue, and is environmentally friendly and low in cost.

[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-strength flexible cable insulation material, characterized in that, Includes the following steps: S1. Dry 50-70 parts by weight of linear low-density polyethylene, 20-30 parts by weight of ethylene-vinyl acetate copolymer and 10-20 parts by weight of ethylene-octene copolymer at 800℃-90℃ and vacuum degree of -0.08 to -0.09MPa for 4-6 hours. S2. Preheat 3-8 parts of nano-silica and 1-3 parts of hydroxylated multi-walled carbon nanotubes at 100℃-120℃ for 10min-15min, add 0.5-1.5 parts of silane coupling agent KH550, and mix at high speed using a high-speed mixer for 20min-30min to obtain surface-modified composite filler. S3. Add the pretreated matrix resin to a twin-screw extruder and melt-plasticize at 140℃-160℃ for 3-5 minutes. Add surface-modified composite filler, 0.2-0.5 parts of antioxidant 1010, 0.1-0.3 parts of antioxidant 168 and 0.5-1.0 parts of ultraviolet absorber UV-327, and blend at 200-300 r / min for 10-15 minutes. S4. Add 1.5-3.0 parts of vinyltrimethoxysilane and 0.05-0.15 parts of dicumyl peroxide, and perform a grafting reaction at 160℃-170℃ for 5 min-8 min to obtain a grafted blend. S5. Extrude the grafted blend at 150℃-165℃, cool it with water, and pelletize it to obtain grafted masterbatch. S6. After drying the grafted masterbatch, it is extruded and coated onto the surface of the cable conductor at 140℃-155℃, and then crosslinked in warm water at 80℃-90℃ for 12-24 hours to obtain a high-strength flexible cable insulation material.

2. The method for preparing a high-strength flexible cable insulation material according to claim 1, characterized in that: The linear low-density polyethylene in step S1 has a melt index of 1-3 g / 10 min, the vinyl acetate content in the ethylene-vinyl acetate copolymer is 18%-28% by mass, and the octene content in the ethylene-octene copolymer is 20%-30% by mass.

3. The method for preparing a high-strength flexible cable insulation material according to claim 1, characterized in that: The average particle size of the nano-silica in step S2 is 15nm-30nm, the outer diameter of the hydroxylated multi-walled carbon nanotubes is 8nm-15nm, the length is 10μm-30μm, and the hydroxyl content is 2wt%-4wt%.

4. The method for preparing a high-strength flexible cable insulation material according to claim 1, characterized in that: In step S2, the speed of the high-speed mixer is 2000 r / min-3000 r / min, and the silane coupling agent KH550 is added by dropping, with a dropping time of 5 min-10 min.

5. The method for preparing a high-strength flexible cable insulation material according to claim 1, characterized in that: In step S3, the temperatures of each zone of the twin-screw extruder are as follows: Zone 1 140℃-145℃, Zone 2 145℃-150℃, Zone 3 150℃-155℃, Zone 4 155℃-160℃, and Die head 155℃-160℃.

6. The method for preparing a high-strength flexible cable insulation material according to claim 1, characterized in that: The mass ratio of the initiator dicumyl peroxide to vinyltrimethoxysilane in step S4 satisfies the following formula: ; In the formula: For the mass of dicumyl peroxide, The mass of vinyltrimethoxysilane.

7. The method for preparing a high-strength flexible cable insulation material according to claim 1, characterized in that: In step S5, the pelletizer rotates at a speed of 300 r / min to 500 r / min, and the resulting grafted masterbatch has a particle size of 2 mm to 4 mm.

8. The method for preparing a high-strength flexible cable insulation material according to claim 1, characterized in that: In step S6, the grafted masterbatch is vacuum dried at 90℃-100℃ for 2h-3h, the screw speed of the cable extruder is 60r / min-100r / min, and the thickness of the extruded insulation layer is 0.5mm-2.0mm.

9. The method for preparing a high-strength flexible cable insulation material according to claim 1, characterized in that: During the warm water crosslinking process in step S6, the conductivity of water is less than 10 μS / cm.

10. The method for preparing a high-strength flexible cable insulation material according to claim 1, characterized in that: After the warm water crosslinking is completed in step S6, the insulating material is dried with hot air at 60℃-70℃ for 4h-6h.

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