Aging-resistant overhead insulated cable

Abstract

The application provides an anti-aging overhead insulated cable, and belongs to the technical field of cables, comprising a conductor, an insulation layer and an outer sheath; wherein the insulation layer is composed of a three-layer structure, and the inner shielding layer, the main insulation layer and the outer protective layer are sequentially arranged from inside to outside; the inner shielding layer is prepared from carbon black modified cross-linked polyethylene, and the thickness is 0.5-1.2 mm; the main insulation layer is a nano zinc oxide-silicon rubber composite material, 5-8 wt% of nano zinc oxide particles are dispersed in the silicon rubber, and the thickness of the main insulation layer is 2-3.5 mm; the outer protective layer is prepared from polyolefin modified by an ultraviolet absorber. The anti-aging overhead insulated cable has the advantages that through the optimization of multi-layer materials and the structural design, the cable has the advantages of anti-aging, weather resistance, high mechanical strength and stable electrical performance.

Description

Technical Field

[0001] This invention belongs to the field of cable technology, and more specifically, relates to an aging-resistant overhead insulated cable. Background Technology

[0002] Overhead insulated cables, as a crucial component of power transmission, are widely used in urban power grids, rural power grids, and industrial power applications. However, traditional overhead insulated cables face multiple challenges when exposed to the outdoor environment for extended periods, including ultraviolet radiation, temperature variations, humidity corrosion, and mechanical stress. This leads to cable aging, decreased insulation performance, and even failure, severely impacting the safety and reliability of power systems. Current technologies often use a single material for cable insulation, such as cross-linked polyethylene (XLPE) or silicone rubber. While these materials offer some insulation performance, they suffer from significant deficiencies in weather resistance, UV aging resistance, and mechanical strength. For example, ordinary XLPE is prone to molecular chain breakage under prolonged UV exposure, resulting in insulation cracking. While silicone rubber has good high-temperature resistance, its low mechanical strength makes it difficult to withstand the tensile and bending stresses encountered during overhead installation. Furthermore, the outer sheath of traditional cables is typically made of a single layer of polyvinyl chloride (PVC) or polyolefin materials, which have limited UV resistance and water resistance. After prolonged use, these materials are prone to powdering and cracking, further accelerating the cable's aging process.

[0003] To address the aforementioned issues, existing technologies attempt to improve cable weather resistance by adding anti-aging agents or UV absorbers. However, these methods often only solve a single problem and cannot comprehensively address the cable's aging resistance, mechanical strength, and electrical performance. For example, some cables improve UV resistance by adding carbon black to the insulation layer, but the addition of carbon black reduces the material's insulation performance. Other cables employ a multi-layered structure design, but insufficient interlayer bonding can easily lead to delamination. Furthermore, the corrosion resistance and conductivity of the conductor are also key factors affecting cable lifespan. Traditional aluminum conductors are prone to electrochemical corrosion in humid environments, leading to increased resistance and even strand breakage. Existing anti-corrosion coating technologies (such as galvanizing or painting) suffer from complex processes or limited effectiveness.

[0004] Therefore, there is an urgent need to develop a new type of aging-resistant overhead insulated cable. Through material innovation and structural optimization, this cable can comprehensively solve problems such as poor weather resistance, insufficient mechanical strength, unstable insulation performance, and easy corrosion of conductors in existing technologies.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide an aging-resistant overhead insulated cable that possesses excellent resistance to ultraviolet aging, high mechanical strength, stable electrical insulation properties, and long-term corrosion resistance, thereby meeting the requirements for long-term reliable operation in overhead laying environments.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] An aging-resistant overhead insulated cable includes a conductor, an insulation layer, and an outer sheath;

[0009] The insulating layer consists of three layers, from the inside out: an inner shielding layer, a main insulating layer, and an outer protective layer.

[0010] The inner shielding layer is made of carbon black modified cross-linked polyethylene with a thickness of 0.5-1.2 mm;

[0011] The main insulation layer is a nano zinc oxide-silicone rubber composite material, wherein 5-8 wt% nano zinc oxide particles are dispersed in the silicone rubber, and the thickness of the main insulation layer is 2-3.5 mm;

[0012] The outer protective layer is made of polyolefin modified with an ultraviolet absorber, wherein the ultraviolet absorber is a benzotriazole compound and the content of the benzotriazole compound is 1.5-3 wt%, and the thickness of the outer protective layer is 0.8-1.5 mm.

[0013] This invention provides an aging-resistant overhead insulated cable, which, through multi-layer material optimization and structural design, fundamentally solves the technical problem that traditional overhead insulated cables are prone to aging, insulation performance degradation, or even failure under long-term exposure to multiple factors such as ultraviolet radiation, temperature changes, humidity erosion, and mechanical stress in outdoor environments. In this invention, the insulation layer is designed as a three-layer structure, consisting of an inner shielding layer, a main insulation layer, and an outer protective layer from the inside out. Each layer employs specific materials and processes, achieving modular functionality and synergistic performance enhancement. Firstly, the inner shielding layer is made of carbon black-modified cross-linked polyethylene, with a thickness controlled between 0.5-1.2 mm. This retains the excellent insulation properties and mechanical strength of cross-linked polyethylene while significantly improving UV resistance through the addition of carbon black. The precise thickness setting ensures a balance between shielding effectiveness and cable flexibility, avoiding the problems of excessive thickness affecting cable bending performance or insufficient thickness reducing shielding effectiveness. Subsequently, the main insulation layer uses a nano-zinc oxide-silicone rubber composite material, with a nano-zinc oxide particle content of 5-8 wt% and a thickness of 2-3.5 mm. This combination fully leverages the high-temperature resistance and weather resistance of silicone rubber, while the introduction of nano-zinc oxide further enhances UV resistance and mechanical strength. The small size and surface effect of nano-zinc oxide allow it to effectively absorb and scatter ultraviolet rays, delaying material aging, while the elasticity of silicone rubber... This ensures the cable can withstand tensile and bending stresses during overhead installation. The outer protective layer is made of polyolefin modified with a UV absorber, specifically a benzotriazole compound at a content of 1.5-3 wt% and a thickness of 0.8-1.5 mm. The highly efficient UV absorption of the benzotriazole compound provides the outermost protective barrier, effectively preventing direct UV damage to the internal materials. Simultaneously, the weather resistance and water resistance of the polyolefin material further enhance the overall durability of the cable. Therefore, the three-layer structure ensures strong interlayer bonding, avoiding the delamination defects common in traditional multi-layer cables, thus guaranteeing the structural stability of the cable during long-term use. Furthermore, the carbon black-modified cross-linked polyethylene of the inner shielding layer not only provides UV resistance but also homogenizes conductivity, effectively preventing partial discharge and improving the cable's electrical safety. The nano-zinc oxide-silicone rubber composite material of the main insulation layer uses nanomaterial dispersion technology to ensure the uniform distribution of nano-zinc oxide particles in the silicone rubber matrix, thus avoiding performance inconsistencies caused by particle agglomeration. Furthermore, by precisely controlling the material ratio and thickness range of each layer, this invention achieves the best balance between electrical performance, mechanical performance and weather resistance of the cable, enabling it to not only meet the harsh environmental requirements of overhead laying, but also maintain stable performance during long-term operation.

[0014] Preferably, as a further specific embodiment, the nano zinc oxide particles have a particle size of 20-50 nm, and the surface of the nano zinc oxide is modified with a silane coupling agent.

[0015] This invention further optimizes the nano-zinc oxide-silicone rubber composite material of the main insulating layer by precisely controlling the morphology and surface properties of the nanomaterials, thereby improving the overall performance of the main insulating layer. The nano-zinc oxide particles have a particle size range of 20-50 nm. This size selection ensures a high specific surface area for the nanoparticles to fully utilize their UV shielding effect while avoiding agglomeration problems caused by excessively small particle sizes. Simultaneously, the surface of the nano-zinc oxide is modified with a silane coupling agent. This modification effectively solves the interfacial compatibility problem between the nanoparticles and the silicone rubber matrix. Through the bridging effect of the silane coupling agent, chemical bonds are formed between the inorganic nanoparticles and the organic polymer, which not only improves the dispersion uniformity of the nano-zinc oxide but also enhances the stress transfer efficiency between the filler and the matrix, enabling the composite material to effectively utilize the reinforcing effect of the nanoparticles when subjected to mechanical loads.

[0016] Preferably, as a further specific embodiment, the ultraviolet absorber of the outer protective layer is 2-(2'-hydroxy-5'-methylphenyl)benzotriazole; a transition layer is provided between the outer protective layer and the main insulating layer, the transition layer being a gradient blend of ultraviolet absorber and silicone rubber, wherein the content of ultraviolet absorber in the transition layer increases from 0.5wt% to 3wt% from the inside to the outside.

[0017] This invention also significantly improves the overall weather resistance and interlayer bonding strength of the cable by introducing gradient functional materials and optimizing the distribution of ultraviolet absorbers between the outer protective layer and the inner insulation layer. Under long-term outdoor exposure conditions, ultraviolet rays often penetrate from microscopic defects in the outer protective layer. The uniformly dispersed ultraviolet absorbers in the transition layer can effectively capture these penetrating ultraviolet photons, forming a "defense-in-depth" system. This invention specifies that the ultraviolet absorber used in the outer protective layer is 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, whose molecular structure... The hydroxyl and benzotriazole rings give it excellent UV absorption capabilities, especially strong absorption of UV light in the 280-400nm wavelength range. The introduction of methyl groups improves compatibility with the polyolefin matrix and avoids the migration and precipitation problems of small molecule additives. More importantly, this invention provides a transition layer between the main insulating layer and the outer protective layer. This transition layer is a gradient blend of UV absorber and silicone rubber, wherein the UV absorber content gradually increases from 0.5wt% in the inner layer (closer to the main insulating layer) to 3wt% in the outer layer (closer to the outer protective layer). This gradient transition effectively alleviates the problem of interfacial stress concentration caused by the difference in polarity between the main insulation layer and the outer protective layer. The continuous change in chemical composition achieves a smooth transition in modulus, greatly reducing the risk of interlayer delamination. Furthermore, the gradient distribution of the UV absorber forms a progressively stronger UV protection system from the inside out, ensuring that the outer protective layer has the strongest UV blocking capability while providing adequate protection for the main insulation layer, achieving optimal performance distribution. In addition, the gradient transition layer cleverly solves the problem of interfacial failure caused by inconsistent aging rates of different materials. Because silicone rubber and polyolefins degrade at different rates under UV radiation, traditional structures are prone to stress cracks at the interface, while the gradient transition makes the aging processes of the two materials more coordinated and synchronized. At the same time, this invention also limits the range of UV absorber content. The initial concentration of 0.5 wt% in the inner layer provides basic protection while avoiding excessive UV absorber affecting the original properties of the silicone rubber; the upper limit of 3 wt% in the outer layer ensures maximum protection without deteriorating other material properties due to excessive additives.

[0018] Therefore, the gradient transition layer design provided by this invention not only solves the technical problem of easy failure of the interlayer interface of traditional cables, but also creatively constructs a multi-level ultraviolet protection system, which significantly extends the service life of the cable in harsh outdoor environments.

[0019] Preferably, as a further specific embodiment, the outer sheath has a three-layer structure, consisting of a water-resistant non-woven fabric, a self-cleaning layer, and an anti-aging polyvinyl chloride layer from the inside out.

[0020] This invention also features a three-layer design innovation for the outer sheath structure. Through the precise combination and hierarchical construction of functional materials, it achieves a synergistic improvement in the waterproof, self-cleaning, and anti-aging performance of the cable's outer sheath. Specifically, the outer sheath is designed as a composite structure consisting of a water-blocking non-woven fabric, a self-cleaning layer, and an anti-aging polyvinyl chloride layer, arranged from the inside out. Each layer is functionally enhanced to address specific environmental challenges. The innermost water-blocking non-woven fabric employs a high-density fiber network structure, blocking longitudinal water penetration through capillary action. Its unique, fluffy three-dimensional structure not only provides excellent water-blocking performance but also buffers mechanical stress, protecting the internal insulation layer. The middle self-cleaning layer uses titanium dioxide nanoparticle-modified polyurethane material, utilizing the photocatalytic properties of titanium dioxide to... The three-layer structure design removes surface contaminants, keeps the cable clean, and reduces the risk of contamination flashover. The outermost anti-aging polyvinyl chloride layer is constructed with a specific ratio of antioxidants and light stabilizers to create a long-lasting anti-aging barrier. This three-layer structure design assigns the three major functions of waterproofing, self-cleaning, and anti-aging to dedicated material layers, avoiding the performance trade-offs caused by multi-functionality of a single material. In addition, the non-woven fabric and the polyurethane self-cleaning layer form a mechanical interlocking structure through a thermal composite process, while the self-cleaning layer and the polyvinyl chloride layer are firmly bonded through molecular-level compatibility, ensuring the integrity of the multi-layer structure during long-term use. Furthermore, the flexibility of the non-woven fabric, the elasticity of the polyurethane, and the rigidity of the polyvinyl chloride form a gradient change, which allows the stress of the cable to be reasonably distributed when it is bent.

[0021] Preferably, as a further specific embodiment, the self-cleaning layer is titanium dioxide nanoparticle-modified polyurethane, the titanium dioxide content is 2-5 wt%, and the titanium dioxide is activated by ultraviolet light.

[0022] This invention also involves further technological innovation and parameter optimization of the self-cleaning layer. Through precise modification of titanium dioxide nanoparticles and ultraviolet light activation treatment, the cable outer sheath acquires a long-lasting and highly efficient self-cleaning capability. The addition of 2-5 wt% titanium dioxide ensures the self-cleaning effect while avoiding the accelerated aging of the matrix that may result from excessive photocatalyst. This is because the reactive oxygen species generated during the photocatalytic process of titanium dioxide, while decomposing pollutants, may also attack polymer molecular chains. When the content is below 2 wt%, the photocatalytic effect is insufficient, making it difficult to achieve an effective self-cleaning function; while exceeding 5 wt% will lead to a significant decrease in the mechanical properties of the polyurethane matrix, and the nanoparticles are prone to agglomeration, affecting the uniformity of dispersion. Furthermore, titanium dioxide... Nanoparticles must undergo ultraviolet light activation treatment to overcome the technical bottleneck of conventional titanium dioxide photocatalysts requiring continuous ultraviolet excitation to maintain activity. Pretreatment creates more oxygen vacancies and active sites on the surface of titanium dioxide, significantly improving its catalytic efficiency under weak or intermittent light conditions. In addition, the modified polyurethane composite material design demonstrates multiple advantages. First, the polyurethane matrix itself has excellent weather resistance, elasticity, and adhesion, which can well adapt to the deformation stress caused by cable bending and temperature changes. Meanwhile, the uniformly dispersed titanium dioxide nanoparticles form photocatalytic active sites on the surface, decomposing organic pollutants such as dust, algae, and various organic deposits attached to the cable surface through the interaction of photogenerated electron-hole pairs.

[0023] Preferably, as a further specific embodiment, the anti-aging polyvinyl chloride layer contains 0.5-1.2 wt% antioxidant and 1-3 wt% hindered amine light stabilizer.

[0024] This invention also features a more refined formulation design for the anti-aging polyvinyl chloride layer. Through the scientific compounding of antioxidants and hindered amine light stabilizers, a synergistic protection system is constructed, enabling the cable outer sheath to achieve breakthrough long-term anti-aging performance. The antioxidants primarily target thermo-oxidative aging during processing and use, interrupting chain reactions by capturing free radicals. Their content is controlled at 0.5-1.2 wt%, effectively inhibiting material thermal degradation while avoiding migration and precipitation problems caused by excessive addition. The hindered amine light stabilizers specifically address outdoor ultraviolet radiation, capturing UV-excited active substances by forming stable nitrile and oxygen free radicals. An addition amount of 1-3 wt% ensures protection under different atmospheric conditions. Both stabilizers provide long-lasting UV protection under various weather conditions. The synergistic effect of these two stabilizers results in superior performance. The antioxidant mainly works within the material, while the hindered amine light stabilizer is more focused on surface protection. Together, they form a three-dimensional protective network to resist the aging effects of heat, oxygen, light, and other factors. Therefore, this invention also emphasizes the ratio of the two additives. When the mass ratio of antioxidant to hindered amine light stabilizer is maintained in the range of 1:2 to 1:3, the material exhibits the best aging resistance. This is because the hindered amine light stabilizer consumes some antioxidants during its function, and an appropriate excess is needed to ensure long-term protective effects.

[0025] Preferably, as a further specific embodiment, the conductor is a compacted circular aluminum conductor, and the surface of the compacted circular aluminum conductor is coated with a graphene coating of 0.05-0.1 mm thickness.

[0026] This invention also improves the conductor structure by introducing a graphene coating, which significantly enhances the overall performance of the compacted circular aluminum conductor. The conductor is a compacted circular aluminum conductor coated with a 0.05-0.1 mm thick graphene coating. This solves the technical problem of electrochemical corrosion and increased contact resistance in traditional aluminum conductors in humid environments. The graphene coating, with its single-atom-layer two-dimensional structure, forms a dense physical barrier layer, effectively isolating the aluminum substrate from external moisture and electrolytes. Simultaneously, graphene's excellent conductivity ensures uniform current distribution, avoiding electrochemical corrosion caused by localized current concentration. The 0.05-0.1 mm thickness range ensures complete coverage and protection without significantly increasing the conductor diameter and affecting the overall cable structure design. From a material interface perspective, graphene and the aluminum substrate form a stable bond through physical adsorption and mechanical interlocking. This bonding method ensures the coating's strength while avoiding the adverse effects of high-temperature treatment on the mechanical properties of the aluminum conductor.

[0027] Preferably, as a further specific embodiment, the graphene coating is further embedded with silver nanoparticles, the silver nanoparticles having a particle size of 10-30 nm and the silver nanoparticle content being 5-15% of the graphene mass.

[0028] Furthermore, this invention enhances the functionality of the graphene coating by embedding nano-silver particles, imparting additional antibacterial and conductivity-enhancing properties to the conductor coating. Specifically, the embedding of nano-silver particles with a particle size of 10-30 nm is limited to the graphene coating, with the content controlled within the range of 5-15% of the graphene mass. This organically combines the advantageous properties of the two nanomaterials, giving the composite coating multiple functions. The addition of nano-silver particles significantly improves the coating's antibacterial performance; their specific particle size range ensures maximum specific surface area and exposure of active sites, effectively inhibiting microorganisms on the cable surface. This biofilm formation is particularly important in humid and rainy regions to prevent the degradation of insulation performance caused by biofilm formation. At the same time, the conductive network formed between the nano-silver and graphene further reduces the contact resistance. A mass ratio of 5-15% can form a continuous conductive path and avoid the agglomeration problem that may be caused by excessive silver particles. In addition, the selection of silver particle size of 10-30nm is particularly critical. Particles that are too small are prone to oxidation and loss of activity, while particles that are too large are difficult to disperse evenly between graphene layers. This size range ensures the stability of the nano-silver and allows it to be well embedded in the layered structure of graphene.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The present invention provides an aging-resistant overhead insulated cable. Through multi-layer material optimization and structural design, the cable has the characteristics of aging resistance, weather resistance, high mechanical strength and stable electrical performance. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] To more clearly illustrate the technical solutions in this invention, specific embodiments are described below.

[0033] Example 1

[0034] The specific preparation process of the aging-resistant overhead insulated cable of the present invention is as follows:

[0035] 1. Conductor preparation

[0036] A compacted round aluminum conductor is used as the core of the cable, with a conductor diameter of 8mm. First, the surface of the aluminum conductor is pretreated: it is ultrasonically cleaned at 60℃ for 15 minutes using an alkaline cleaning agent (5% NaOH solution) to remove the surface oxide layer and oil.

[0037] Rinse with deionized water until neutral, then dry in an oven at 80°C for 2 hours;

[0038] The aluminum conductor is pressed tightly using a cold pressing process;

[0039] Preparation of graphene dispersion

[0040] Graphene was prepared by redox method: graphene oxide (GO) was dispersed in deionized water (concentration 2 mg / mL);

[0041] Add 0.1 mol / L vitamin C as a reducing agent and react in a 95°C water bath for 6 hours;

[0042] After centrifugation and washing, a graphene aqueous dispersion (solid content 1.5wt%) was obtained, and ultrasonic treatment (power 300W) was performed for 30 minutes to ensure uniform dispersion.

[0043] Nano-silver composite modification

[0044] Silver nitrate solution (0.1 mol / L) was mixed with the above graphene dispersion at a mass ratio of 0.05:1, and sodium citrate (0.5 wt%) was added as a stabilizer. The mixture was stirred in a water bath at 60°C for 2 hours.

[0045] The reaction process was monitored by ultraviolet-visible spectroscopy until a significant silver plasma resonance absorption peak appeared at 410 nm to obtain the composite dispersion.

[0046] Conductor surface pretreatment

[0047] The compressed aluminum conductor was subjected to plasma cleaning (Ar atmosphere, power 200W, treatment for 5 minutes), and then a porous aluminum oxide layer was formed on the surface by anodizing.

[0048] Coating preparation process

[0049] Electrophoretic deposition method was adopted: the composite dispersion was placed in a stainless steel electrolytic cell, an aluminum conductor was set as the cathode, a DC voltage of 20V was applied, the deposition time was 3 minutes, and the coating thickness was controlled to be 0.05±0.01mm.

[0050] Under nitrogen protection, heat treatment at 250°C for 1 hour was performed to improve the density of the coating.

[0051] Post-processing

[0052] Cold isostatic pressing was used to further increase the coating density, and surface polishing was used to ensure coating uniformity. Subsequently, SEM and EDS were used to confirm that the nano-silver particles (10 nm in diameter) were uniformly distributed in the graphene layer.

[0053] 2. Insulation layer preparation: The inner shielding layer, the main insulation layer, and the outer protective layer are formed sequentially;

[0054] (1) Inner shielding layer

[0055] Raw materials: 100 parts cross-linked polyethylene (XLPE) base material, 3 parts conductive carbon black (particle size 30nm), 1.5 parts dicumyl peroxide (DCP) cross-linking agent;

[0056] Processing technology: The raw materials are mixed in an internal mixer at 120°C for 15 minutes, and then extruded through a twin-screw extruder to coat the conductor surface with a thickness controlled at 0.5±0.05mm. Subsequently, the mixture is cross-linked for 30 minutes through a steam cross-linking pipeline (pressure 1.2MPa, temperature 200°C).

[0057] (2) Main insulation layer

[0058] Raw material ratio: 100 parts of methyl vinyl silicone rubber (VMQ), 5 parts of nano zinc oxide (particle size 20nm, modified with KH-550 silane coupling agent), 2 parts of hydroxyl silicone oil, and 0.8 parts of vulcanizing agent bis(2,5)5.

[0059] Processing technology: Mix nano zinc oxide particles with silane coupling agent (KH-550) at a mass ratio of 1:0.05 and stir at 60℃ for 30 minutes;

[0060] The modified nano zinc oxide was dried in an oven at 80°C for 2 hours to remove residual solvent;

[0061] Take 100 parts of methyl vinyl silicone rubber base material, add 2 parts of hydroxyl silicone oil, and premix on a two-roll mill for 5 minutes to form a uniform mixture;

[0062] Add 5 parts of the dried and modified nano zinc oxide to the mixture and continue to mix on a two-roll mill for 15 minutes to ensure that the nanoparticles are evenly dispersed and avoid agglomeration.

[0063] Finally, add 0.8 parts of the vulcanizing agent 25 and mix for 5 minutes until completely uniform;

[0064] The mixed material is extruded and coated onto the outside of the inner shielding layer, with the thickness of the main insulation layer controlled at 3.5 mm.

[0065] Subsequently, it is vulcanized in hot air at 160°C for 20 minutes to crosslink and cure the methyl vinyl silicone rubber, forming a stable main insulation layer structure.

[0066] (3) Transition layer

[0067] Raw materials: A gradient blend of ultraviolet absorber (2-(2'-hydroxy-5'-methylphenyl)benzotriazole) and silicone rubber (VMQ) is used, with the ultraviolet absorber content gradually increasing from 0.5 wt% in the inner layer (close to the main insulation layer) to 3 wt% in the outer layer (close to the outer protective layer).

[0068] The specific gradient distribution is designed as follows:

[0069] Inner layer (0.5wt%): 100 parts silicone rubber, 0.5 parts ultraviolet absorber, 2 parts hydroxyl silicone oil;

[0070] Intermediate layer (1.5wt%): 100 parts silicone rubber, 1.5 parts UV absorber, 2 parts hydroxyl silicone oil;

[0071] Outer layer (3wt%): 100 parts silicone rubber, 3 parts ultraviolet absorber, 2 parts hydroxyl silicone oil;

[0072] Processing technology: The UV absorber is refined to a particle size of <5μm by a ball mill, and then the UV absorber and silicone rubber base material are dried separately to avoid moisture affecting dispersibility; three parallel internal mixers are used to simultaneously mix and prepare blends of 0.5wt%, 1.5wt%, and 3wt% respectively. Mixing conditions: temperature 40℃, time 15 minutes; the three blends are simultaneously extruded through a multi-layer co-extruder (equipped with a gradient feeding system) to form a continuous gradient transition layer with a thickness of 0.2mm; then, after the main insulation layer is vulcanized (before it is completely cooled to room temperature), the transition layer is immediately bonded to the surface of the main insulation layer by a hot pressing process (temperature 150℃, pressure 0.5MPa, time 30 seconds).

[0073] (4) Outer protective layer

[0074] Raw material ratio: 100 parts low-density polyethylene (LDPE), 1.5 parts 2-(2'-hydroxy-5'-methylphenyl)benzotriazole;

[0075] Processing technology: The raw materials are mixed in a high-speed mixer for 10 minutes, and then the coating transition layer is extruded through a single screw extruder with a thickness of 0.8±0.05mm. The temperature of the cooling water tank is controlled below 30℃.

[0076] (5) Outer layer

[0077] Prepare an outer sheath that wraps around the surface of the insulation layer:

[0078] Water-blocking nonwoven fabric layer: Polyester fiber nonwoven fabric (50g / m²) is selected. 2 It is bonded to the insulation layer using a hot melt adhesive coating device (temperature 180℃);

[0079] Self-cleaning layer: 100 parts polyurethane (TPU) and 2 parts ultraviolet-activated titanium dioxide (particle size 25nm) are extruded and coated with a water-blocking non-woven fabric layer with a thickness of 0.3mm through a twin-screw extruder (temperature 180-200℃).

[0080] Anti-aging PVC layer: 100 parts PVC resin, 0.5 parts antioxidant (phosphite esters), 1 part hindered amine light stabilizer (HALS), formed by extrusion, with a thickness of 0.7 mm.

[0081] Example 2

[0082] The specific preparation process of the aging-resistant overhead insulated cable of the present invention is as follows:

[0083] 1. Conductor preparation

[0084] A compacted round aluminum conductor with a diameter of 8mm is used as the cable core. The aluminum conductor surface is first pretreated by ultrasonic cleaning at 60℃ for 15 minutes using an alkaline cleaning agent (5% NaOH solution) to remove the surface oxide layer and oil.

[0085] Rinse with deionized water until neutral, then dry in an oven at 80°C for 2 hours;

[0086] The aluminum conductor is pressed tightly using a cold pressing process;

[0087] Preparation of graphene dispersion

[0088] Graphene was prepared by redox method: graphene oxide (GO) was dispersed in deionized water (concentration 2 mg / mL);

[0089] Add 0.1 mol / L vitamin C as a reducing agent and react in a 95°C water bath for 6 hours;

[0090] After centrifugation and washing, a graphene aqueous dispersion (solid content 1.5wt%) was obtained, and ultrasonic treatment (power 300W) was performed for 30 minutes to ensure uniform dispersion.

[0091] Nano-silver composite modification

[0092] Silver nitrate solution (0.1 mol / L) was mixed with the above graphene dispersion at a mass ratio of 0.15:1, and sodium citrate (0.5 wt%) was added as a stabilizer. The mixture was stirred in a water bath at 60°C for 2 hours.

[0093] The reaction process was monitored by ultraviolet-visible spectroscopy until a significant silver plasma resonance absorption peak appeared at 410 nm to obtain the composite dispersion.

[0094] Conductor surface pretreatment

[0095] The compressed aluminum conductor was subjected to plasma cleaning (Ar atmosphere, power 200W, treatment for 5 minutes), and then a porous aluminum oxide layer was formed on the surface by anodizing.

[0096] Coating preparation process

[0097] Electrophoretic deposition method was adopted: the composite dispersion was placed in a stainless steel electrolytic cell, an aluminum conductor was set as the cathode, a DC voltage of 20V was applied, the deposition time was 3 minutes, and the coating thickness was controlled to be 0.1±0.01mm;

[0098] Heat treatment at 250°C for 1 hour under nitrogen protection to improve coating density.

[0099] Post-processing

[0100] Cold isostatic pressing was used to further increase the coating density, and surface polishing was used to ensure coating uniformity. Subsequently, SEM and EDS were used to confirm that the nano-silver particles (particle size 30) were uniformly distributed in the graphene layer.

[0101] 2. Insulation layer preparation: The inner shielding layer, the main insulation layer, and the outer protective layer are formed sequentially;

[0102] (1) Inner shielding layer

[0103] Raw materials: 100 parts cross-linked polyethylene (XLPE) base material, 3 parts conductive carbon black (particle size 30nm), 1.5 parts dicumyl peroxide (DCP) cross-linking agent;

[0104] Processing technology: The raw materials are mixed in an internal mixer at 120°C for 15 minutes, and then extruded through a twin-screw extruder to coat the conductor surface with a thickness controlled at 1.2±0.05mm. Subsequently, the mixture is cross-linked for 30 minutes through a steam cross-linking pipeline (pressure 1.2MPa, temperature 200°C).

[0105] (2) Main insulation layer

[0106] Raw material ratio: 100 parts of methyl vinyl silicone rubber (VMQ), 8 parts of nano zinc oxide (particle size 50nm, modified with KH-550 silane coupling agent), 2 parts of hydroxyl silicone oil, and 0.8 parts of vulcanizing agent bis(2,5)5.

[0107] Processing technology: Nano zinc oxide particles are mixed with silane coupling agent (KH-550) at a mass ratio of 1:0.05 and stirred at 60℃ for 30 minutes;

[0108] The modified nano zinc oxide was dried in an oven at 80°C for 2 hours to remove residual solvent;

[0109] Take 100 parts of methyl vinyl silicone rubber base material, add 2 parts of hydroxyl silicone oil, and premix on a two-roll mill for 5 minutes to form a uniform mixture;

[0110] Add 8 parts of the dried and modified nano zinc oxide to the mixture and continue to mix on a two-roll mill for 15 minutes to ensure that the nanoparticles are evenly dispersed and avoid agglomeration.

[0111] Finally, add 0.8 parts of the vulcanizing agent 25 and mix for 5 minutes until completely uniform;

[0112] The mixed material is extruded and coated onto the outside of the inner shielding layer, with the thickness of the main insulation layer controlled at 2 mm. Then, it is vulcanized in hot air at 160°C for 20 minutes to crosslink and cure the methyl vinyl silicone rubber, forming a stable main insulation layer structure.

[0113] (3) Transition layer

[0114] Raw materials: A gradient blend of ultraviolet absorber (2-(2'-hydroxy-5'-methylphenyl)benzotriazole) and silicone rubber (VMQ) is used, with the ultraviolet absorber content gradually increasing from 0.5 wt% in the inner layer (close to the main insulation layer) to 3 wt% in the outer layer (close to the outer protective layer).

[0115] The specific gradient distribution is designed as follows:

[0116] Inner layer (0.5wt%): 100 parts silicone rubber, 0.5 parts ultraviolet absorber, 2 parts hydroxyl silicone oil;

[0117] Intermediate layer (1.5wt%): 100 parts silicone rubber, 1.5 parts UV absorber, 2 parts hydroxyl silicone oil;

[0118] Outer layer (3wt%): 100 parts silicone rubber, 3 parts ultraviolet absorber, 2 parts hydroxyl silicone oil;

[0119] Processing technology: The UV absorber is refined to a particle size of <5μm by a ball mill, and then the UV absorber and silicone rubber base material are dried separately to avoid moisture affecting dispersibility; three parallel internal mixers are used to simultaneously mix and prepare blends of 0.5wt%, 1.5wt%, and 3wt% respectively. Mixing conditions: temperature 40℃, time 15 minutes; the three blends are simultaneously extruded through a multi-layer co-extruder (equipped with a gradient feeding system) to form a continuous gradient transition layer with a thickness of 0.2mm; then, after the main insulation layer is vulcanized (before it is completely cooled to room temperature), the transition layer is immediately bonded to the surface of the main insulation layer by a hot pressing process (temperature 150℃, pressure 0.5MPa, time 30 seconds).

[0120] (4) Outer protective layer

[0121] Raw material ratio: 100 parts low-density polyethylene (LDPE), 3 parts 2-(2'-hydroxy-5'-methylphenyl)benzotriazole;

[0122] Processing technology: The raw materials are mixed in a high-speed mixer for 10 minutes, and then the coating transition layer is extruded through a single screw extruder with a thickness of 1.5±0.05mm. The temperature of the cooling water tank is controlled below 30℃.

[0123] (5) Outer layer

[0124] Form an outer sheath that wraps around the surface of the insulation layer:

[0125] Water-blocking nonwoven fabric layer: Polyester fiber nonwoven fabric (50g / m²) is selected. 2 It is bonded to the insulation layer using a hot melt adhesive coating device (temperature 180℃);

[0126] Self-cleaning layer: 100 parts polyurethane (TPU) and 5 parts ultraviolet-activated titanium dioxide (particle size 25nm) are extruded and coated with a water-blocking non-woven fabric layer with a thickness of 0.3mm through a twin-screw extruder (temperature 180-200℃).

[0127] Anti-aging PVC layer: 100 parts PVC resin, 1.2 parts antioxidant (phosphite esters), 3 parts hindered amine light stabilizer (HALS), formed by extrusion, with a thickness of 0.7 mm.

[0128] Example 3

[0129] The specific preparation process of the aging-resistant overhead insulated cable of the present invention is as follows:

[0130] 1. Conductor preparation

[0131] A compacted round aluminum conductor with a diameter of 8mm is used as the cable core. The aluminum conductor surface is first pretreated by ultrasonic cleaning at 60℃ for 15 minutes using an alkaline cleaning agent (5% NaOH solution) to remove the surface oxide layer and oil.

[0132] Rinse with deionized water until neutral, then dry in an oven at 80°C for 2 hours;

[0133] The aluminum conductor is pressed tightly using a cold pressing process;

[0134] Preparation of graphene dispersion

[0135] Graphene was prepared by redox method: graphene oxide (GO) was dispersed in deionized water (concentration 2 mg / mL);

[0136] Add 0.1 mol / L vitamin C as a reducing agent and react in a 95°C water bath for 6 hours;

[0137] After centrifugation and washing, a graphene aqueous dispersion (solid content 1.5wt%) was obtained, and ultrasonic treatment (power 300W) was performed for 30 minutes to ensure uniform dispersion.

[0138] Nano-silver composite modification

[0139] Silver nitrate solution (0.1 mol / L) was mixed with the above graphene dispersion at a mass ratio of 0.1:1, and sodium citrate (0.5 wt%) was added as a stabilizer. The mixture was stirred in a water bath at 60°C for 2 hours.

[0140] The reaction process was monitored by ultraviolet-visible spectroscopy until a significant silver plasma resonance absorption peak appeared at 410 nm to obtain the composite dispersion.

[0141] Conductor surface pretreatment

[0142] The compressed aluminum conductor was subjected to plasma cleaning (Ar atmosphere, power 200W, treatment for 5 minutes), and then a porous aluminum oxide layer was formed on the surface by anodizing.

[0143] Coating preparation process

[0144] Electrophoretic deposition method was adopted: the composite dispersion was placed in a stainless steel electrolytic cell, an aluminum conductor was set as the cathode, a DC voltage of 20V was applied, the deposition time was 3 minutes, and the coating thickness was controlled to be 0.08±0.01mm;

[0145] Heat treatment at 250°C for 1 hour under nitrogen protection to improve coating density.

[0146] Post-processing

[0147] Cold isostatic pressing was used to further increase the coating density, and surface polishing was used to ensure coating uniformity. Subsequently, SEM and EDS were used to confirm that the nano-silver particles (particle size 20) were uniformly distributed in the graphene layer.

[0148] 2. Insulation layer preparation: The inner shielding layer, the main insulation layer, and the outer protective layer are formed sequentially;

[0149] (1) Inner shielding layer

[0150] Raw materials: 100 parts cross-linked polyethylene (XLPE) base material, 3 parts conductive carbon black (particle size 30nm), 1.5 parts dicumyl peroxide (DCP) cross-linking agent;

[0151] Processing technology: The raw materials are mixed in an internal mixer at 120°C for 15 minutes, and then extruded through a twin-screw extruder to coat the conductor surface with a thickness controlled at 1.0±0.05mm. Subsequently, the mixture is cross-linked for 30 minutes through a steam cross-linking pipeline (pressure 1.2MPa, temperature 200°C).

[0152] (2) Main insulation layer

[0153] Raw material ratio: 100 parts of methyl vinyl silicone rubber (VMQ), 7 parts of nano zinc oxide (particle size 50nm, modified with KH-550 silane coupling agent), 2 parts of hydroxyl silicone oil, and 0.8 parts of vulcanizing agent bis(2,5)5.

[0154] Processing technology: Nano zinc oxide particles are mixed with silane coupling agent (KH-550) at a mass ratio of 1:0.05 and stirred at 60℃ for 30 minutes;

[0155] The modified nano zinc oxide was dried in an oven at 80°C for 2 hours to remove residual solvent;

[0156] Take 100 parts of methyl vinyl silicone rubber base material, add 2 parts of hydroxyl silicone oil, and premix on a two-roll mill for 5 minutes to form a uniform mixture;

[0157] Add 7 parts of the dried and modified nano zinc oxide to the mixture and continue to mix on a two-roll mill for 15 minutes to ensure that the nanoparticles are evenly dispersed and avoid agglomeration.

[0158] Finally, add 0.8 parts of the vulcanizing agent 25 and mix for 5 minutes until completely uniform;

[0159] The mixed material is extruded and coated onto the outside of the inner shielding layer, with the thickness of the main insulation layer controlled at 3 mm. Then, it is vulcanized in hot air at 160°C for 20 minutes to crosslink and cure the methyl vinyl silicone rubber, forming a stable main insulation layer structure.

[0160] (3) Transition layer

[0161] Raw materials: A gradient blend of ultraviolet absorber (2-(2'-hydroxy-5'-methylphenyl)benzotriazole) and silicone rubber (VMQ) is used, with the ultraviolet absorber content gradually increasing from 0.5 wt% in the inner layer (close to the main insulation layer) to 3 wt% in the outer layer (close to the outer protective layer).

[0162] The specific gradient distribution is designed as follows:

[0163] Inner layer (0.5wt%): 100 parts silicone rubber, 0.5 parts ultraviolet absorber, 2 parts hydroxyl silicone oil;

[0164] Intermediate layer (1.5wt%): 100 parts silicone rubber, 1.5 parts UV absorber, 2 parts hydroxyl silicone oil;

[0165] Outer layer (3wt%): 100 parts silicone rubber, 3 parts ultraviolet absorber, 2 parts hydroxyl silicone oil;

[0166] Processing technology: The UV absorber is refined to a particle size of <5μm by a ball mill, and then the UV absorber and silicone rubber base material are dried separately to avoid moisture affecting dispersibility; three parallel internal mixers are used to simultaneously mix and prepare blends of 0.5wt%, 1.5wt%, and 3wt% respectively. Mixing conditions: temperature 40℃, time 15 minutes; the three blends are simultaneously extruded through a multi-layer co-extruder (equipped with a gradient feeding system) to form a continuous gradient transition layer with a thickness of 0.2mm; then, after the main insulation layer is vulcanized (before it is completely cooled to room temperature), the transition layer is immediately bonded to the surface of the main insulation layer by a hot pressing process (temperature 150℃, pressure 0.5MPa, time 30 seconds).

[0167] (4) Outer protective layer

[0168] Raw material ratio: 100 parts low-density polyethylene (LDPE), 2 parts 2-(2'-hydroxy-5'-methylphenyl)benzotriazole;

[0169] Processing technology: The raw materials are mixed in a high-speed mixer for 10 minutes, and then the coating transition layer is extruded through a single screw extruder with a thickness of 1.0±0.05mm. The temperature of the cooling water tank is controlled below 30℃.

[0170] (5) Outer layer

[0171] Form an outer sheath that wraps around the surface of the insulation layer:

[0172] Water-blocking nonwoven fabric layer: Polyester fiber nonwoven fabric (50g / m²) is selected. 2 It is bonded to the insulation layer using a hot melt adhesive coating device (temperature 180℃);

[0173] Self-cleaning layer: 100 parts polyurethane (TPU), 3 parts UV-activated titanium dioxide (particle size 25nm), extruded and coated with a water-blocking non-woven fabric layer through a twin-screw extruder (temperature 180-200℃), with a thickness of 0.3mm.

[0174] Anti-aging PVC layer: 100 parts PVC resin, 1 part antioxidant (phosphite ester), 2 parts hindered amine light stabilizer (HALS), formed by extrusion, with a thickness of 0.7 mm.

[0175] Comparative Example 1

[0176] The specific implementation steps are the same as in Example 3, except that the amount of nano zinc oxide particles in the main insulating layer in Example 3 is adjusted to 1 part.

[0177] Comparative Example 2

[0178] The specific implementation steps are the same as in Example 3, except that the amount of nano zinc oxide particles in the main insulation layer in Example 3 is adjusted to 10 parts.

[0179] Comparative Example 3

[0180] The specific implementation steps are the same as in Example 3, except that the thickness of the inner shielding layer in Example 3 is adjusted to 0.1 mm.

[0181] Comparative Example 4

[0182] The specific implementation steps are the same as in Example 3, except that the thickness of the inner shielding layer in Example 3 is adjusted to 5mm.

[0183] Comparative Example 5

[0184] The specific implementation steps are the same as in Example 3, except that the thickness of the main insulation layer in Example 3 is adjusted to 0.5 mm.

[0185] Comparative Example 6

[0186] The specific implementation steps are the same as in Example 3, except that the thickness of the main insulation layer in Example 3 is adjusted to 10mm.

[0187] Comparative Example 7

[0188] The specific implementation steps are the same as in Example 3, except that the amount of benzotriazole compound in the outer protective layer in Example 3 is adjusted to 0.5 parts.

[0189] Comparative Example 8

[0190] The specific implementation steps are the same as in Example 3, except that the amount of benzotriazole compound in the outer protective layer in Example 3 is adjusted to 5 parts.

[0191] Comparative Example 9

[0192] The specific implementation steps are the same as in Example 3, except that the amount of titanium dioxide used in Example 3 is adjusted to 0.5 parts.

[0193] Comparative Example 10

[0194] The specific implementation steps are the same as in Example 3, except that the amount of titanium dioxide used in Example 3 is adjusted to 10 parts.

[0195] Comparative Example 11

[0196] The specific implementation steps are the same as in Example 3, except that the polyethylene material in the inner shielding layer is not modified and crosslinked with carbon black; that is, the raw material of the inner shielding layer is polyethylene.

[0197] Comparative Example 12

[0198] The specific implementation steps are the same as in Example 3, except that the polyolefin in the outer protective layer is not modified with an ultraviolet absorber.

[0199] Comparative Example 13

[0200] The specific implementation steps are the same as in Example 3, except that the nano zinc oxide in the main insulation layer is not modified by silane coupling agent.

[0201] Comparative Example 14

[0202] The specific implementation steps are the same as in Example 3, except that no transition layer is set between the outer protective layer and the main insulation layer.

[0203] Comparative Example 15

[0204] The specific implementation steps are the same as in Example 3, except that the ultraviolet absorber and silicone rubber in the transition layer are not gradient blended, that is, the content of ultraviolet absorber is 0.5 wt% from the inside to the outside.

[0205] Comparative Example 16

[0206] The specific implementation steps are the same as in Example 3, except that titanium dioxide nanoparticles are not used to modify the polyurethane in the self-cleaning layer.

[0207] Experiment Example 1: Performance Test of Aging-Resistant Overhead Insulated Cables

[0208] The cables prepared in Examples 1-3 and Comparative Examples 1-19 were used as samples for mechanical performance testing, electrical performance testing, aging resistance testing, and environmental adaptability testing. The specific testing procedures are as follows:

[0209] 1 Mechanical performance test

[0210] 1.1 Tensile strength test

[0211] Sample preparation: dumbbell-shaped samples (length ≥ 100 mm, gauge length 25 mm, width 4 mm) were cut from the cable insulation layer and outer sheath prepared in Examples 1-3 and Comparative Examples 1-19, respectively.

[0212] Testing equipment: Universal testing machine (range ≥500N, accuracy ±1%);

[0213] Test steps:

[0214] Clamp both ends of the sample tightly to ensure there is no slippage;

[0215] The specimen was stretched at a constant rate (50 mm / min) until it broke.

[0216] Record the maximum tensile force (N) and calculate the tensile strength (MPa = tensile force / cross-sectional area);

[0217] Data recording: Each test group should contain at least 5 samples, and the average value should be taken.

[0218] 1.2 Elongation at break test

[0219] Test equipment: Same as tensile strength test.

[0220] Test steps:

[0221] Mark the gauge length of the specimen (initial length L) D );

[0222] Stretch until fracture, and measure the gauge length (L1) at fracture.

[0223] Calculate the elongation at break (%) = (L1 - L D ) / L D ×100%;

[0224] Data recording: Tested simultaneously with tensile strength, and the average value was taken;

[0225] 2. Electrical performance testing

[0226] 2.1 Volume Resistivity Test

[0227] Sample preparation: Take the sheet-like samples of cable insulation layer (1 mm thick, 50 mm in diameter) prepared in Examples 1-3 and Comparative Examples 1-19, with clean and uncontaminated surfaces;

[0228] Test equipment: High resistance meter (test voltage 500V);

[0229] Test steps:

[0230] Place the sample between the electrodes, apply a 500V DC voltage, and take a reading after stabilizing for 30 seconds.

[0231] Calculate the volume resistivity (Ω·cm) = resistance value × electrode area / sample thickness;

[0232] Data recording: Each group was tested 3 times, and the median value was taken;

[0233] 2.2 Breakdown Voltage Test

[0234] Sample preparation: Volume resistivity test;

[0235] Testing equipment: Withstand voltage tester (voltage ramp rate 1kV / s);

[0236] Test steps:

[0237] The sample was immersed in insulating oil (to prevent surface flashover);

[0238] The voltage is increased at a rate of 1kV / s until breakdown occurs (current increases sharply);

[0239] Record the breakdown voltage (kV) and calculate the breakdown strength (kV / mm) = breakdown voltage / sample thickness;

[0240] Data recording: Each group was tested 5 times, and the average was taken after removing outliers;

[0241] 3. Aging resistance test

[0242] 3.1 Ultraviolet Aging Test

[0243] Testing equipment: Ultraviolet aging chamber (UVB-313 lamp, irradiance 0.68W / m²) 2 );

[0244] Test steps:

[0245] The cable samples (length ≥ 300 mm) prepared in Examples 1-3 and Comparative Examples 1-19 were fixed in the aging chamber at a distance of 50 cm from the lamp tube;

[0246] Set the loop condition:

[0247] Irradiation phase: 60℃, 4h (UV irradiation);

[0248] Condensation stage: 50℃, 4h (no radiation, high humidity);

[0249] After 1000 hours, the sample was removed and the retention rate of mechanical properties was tested (compared to the initial value).

[0250] Data recording: Record the change rate (%) of tensile strength and elongation at break;

[0251] 3.2 Thermo-oxidative aging test

[0252] Test equipment: constant temperature oven (temperature control accuracy ±1℃);

[0253] Test steps:

[0254] Suspend the sample inside the oven, avoiding contact with the oven walls;

[0255] Set to a constant temperature of 100℃ and age for 168 hours;

[0256] After being removed and cooled to room temperature, the mechanical properties were tested.

[0257] Data recording: Calculate tensile strength and elongation retention (%);

[0258] 4. Environmental adaptability test

[0259] 4.1 Water resistance test

[0260] Test equipment: constant temperature water bath (23±1℃);

[0261] Test steps:

[0262] The cable samples prepared in Examples 1-3 and Comparative Examples 1-19 were immersed in deionized water to ensure complete immersion.

[0263] After soaking for 168 hours, remove and wipe off the surface moisture.

[0264] Immediately test the volume resistivity and calculate the rate of change (%) = (resistivity after aging - initial resistivity) / initial resistivity × 100%;

[0265] Data recording: 3 samples per group, average value taken;

[0266] 4.2 Self-cleaning effect test

[0267] Testing equipment: Contact angle tester, ultraviolet lamp (365nm, 10W);

[0268] Test steps:

[0269] Hydrophobicity test: Add 5 μL of deionized water to the sample surface and measure the static contact angle (°);

[0270] The specific test results are shown in Table 1 below:

[0271] Table 1 Test Results

[0272]

[0273] As shown in the table above, the aging-resistant overhead insulated cables prepared in Examples 1-3 exhibit significant advantages in mechanical properties, electrical properties, and aging resistance. Example 3 represents the optimal experimental scheme. Data from Comparative Examples 1-2 shows that when nano-zinc oxide is insufficient in Comparative Example 1, its UV shielding ability significantly decreases, resulting in a tensile retention rate of only 78.6% after UV aging and a low volume resistivity, indicating that insufficient filler makes it difficult to form an effective protective network. While Comparative Example 2 improved mechanical strength due to its high nano-zinc oxide content, particle agglomeration led to deterioration of insulation performance, with the breakdown voltage dropping to 22.1 kV / mm and the resistivity further decreasing, indicating that the introduction of excessive filler damaged the dielectric properties of the silicone rubber matrix. Furthermore, the water resistance change rate of both examples was higher than that of Example 3, indicating that when the nano-zinc oxide content deviates from the range of 5-8 wt%, the material density decreases, making it easier for moisture to penetrate.

[0274] As can be seen from the data of Comparative Examples 3-4, when the shielding layer of Comparative Example 3 is too thin, the electric field homogenization ability is insufficient, the breakdown voltage is only 20.5kV / mm, and the tensile retention rate after UV aging is significantly reduced, indicating that the thin carbon black modified layer cannot effectively block the penetration of ultraviolet rays. When the mechanical strength and aging performance of Comparative Example 4 are improved due to the increase in thickness, its flexibility decreases, resulting in a lower elongation at break than Example 3, and the excessively thick non-insulating layer leads to a lower volume resistivity. In addition, the water resistance change rate of the two is significantly different (+15.3% and +6.4%), indicating that the thickness of the inner shielding layer needs to be in the range of 0.5-1.2mm to balance the shielding effect and the cable flexibility.

[0275] The data from Comparative Examples 5 and 6 show that in Comparative Example 5, the insulation layer was too thin, resulting in a significant deterioration in both breakdown voltage and volume resistivity, as well as insufficient mechanical strength, indicating that the thin layer could not withstand the mechanical stress of overhead laying. While in Comparative Example 6, although the increased thickness improved electrical performance, the excessively thick main insulation layer led to an increase in cable diameter, decreased flexibility, and a significant increase in cost. The difference in UV aging retention rates between the two examples further demonstrates that a main insulation layer thickness of 2-3.5 mm can ensure insulation reliability while avoiding material waste.

[0276] The data from Comparative Examples 7 and 8 show that in Comparative Example 7, the insufficient benzotriazole content in the outer protective layer resulted in a tensile retention rate of only 74.5% after UV aging, and a low contact angle, indicating a weakened surface protection capability. While Comparative Example 8 improved aging performance due to its high content, excessive additive migration led to a decrease in volume resistivity and increased material brittleness, with a lower elongation at break than Example 3. Furthermore, the water resistance change rates of both examples (+11.6% and +7.8%) were inferior to those of Example 3, indicating that an addition of 1.5-3 wt% benzotriazole can achieve the best balance between protective effect and material stability.

[0277] Data from Comparative Examples 9-10 show that when the titanium dioxide content in the self-cleaning layer of Comparative Example 9 is insufficient, the resulting cable has a contact angle of only 143°, weak photocatalytic activity, and residual surface contaminants. While Comparative Example 10 improves hydrophobicity due to its high content, nanoparticle aggregation causes cracking of the polyurethane matrix, resulting in a decrease in mechanical strength and aging resistance. Furthermore, the difference in resistivity change rates (+6.8% and +11.9%) between the two examples indicates that an addition of 2-5 wt% titanium dioxide can balance self-cleaning function and material integrity.

[0278] As can be seen from the data of Comparative Example 11, when the polyethylene in the inner shielding layer of Comparative Example 11 was not modified and crosslinked with carbon black, its performance was significantly worse than that of Example 3. Its tensile strength was only 12.7 MPa, and its elongation at break was as low as 148%, which was far lower than 23.6 MPa and 302% of Example 3. This indicates that the unmodified polyethylene has insufficient mechanical strength and cannot withstand the tensile and bending stress of overhead laying. In terms of electrical performance, both the volume resistivity and breakdown voltage decreased significantly, indicating that the lack of conductivity homogenization effect of carbon black led to uneven electric field distribution and increased risk of partial discharge. The aging resistance also deteriorated. The tensile retention rate after UV aging was only 60.3%, and the elongation retention rate after thermo-oxidative aging was 58.2%, which was far lower than 95.4% and 94.2% of Example 3, proving that the unmodified polyethylene has extremely poor UV resistance and the molecular chains are easy to break. In addition, the resistivity change rate in the water resistance test was as high as +20.1%, indicating that the material structure was loose and water penetration was serious.

[0279] As can be seen from the data of Comparative Example 12, when the polyolefin in the outer protective layer of Comparative Example 12 was not modified with ultraviolet absorbers, its performance shortcomings were concentrated in aging resistance and surface protection ability. The tensile retention rate after ultraviolet aging was only 68.4%, and the elongation retention rate after thermo-oxidative aging was 66.5%, which was far lower than 95.4% and 94.2% of Example 3, indicating that the outer protective layer without benzotriazole ultraviolet absorbers could not effectively block ultraviolet rays, leading to accelerated aging of the internal insulation layer. In terms of mechanical properties, although the tensile strength and elongation at break were better than those of Comparative Example 11, they were still significantly lower than those of Example 3, indicating that the tensile strength of the unmodified polyolefin was limited. In terms of electrical properties, the decrease in breakdown voltage and volume resistivity was related to the increase in microcracks after material aging. Moreover, the high resistivity change rate in the water resistance test further indicated that the waterproof performance of the unmodified polyolefin was insufficient. The decrease in contact angle also indicated that its surface hydrophobicity was poor and it was easy to adsorb pollutants.

[0280] As can be seen from the data of Comparative Example 13, when the nano-zinc oxide in the main insulation layer of Comparative Example 13 was not modified with silane coupling agent, its performance defects were mainly reflected in the filler dispersion and interfacial bonding force. The tensile strength and elongation at break were lower than those of Example 3, indicating that the unmodified nano-zinc oxide had a weak interfacial bonding with the silicone rubber matrix, resulting in low stress transfer efficiency and a decline in mechanical properties. In terms of electrical properties, the decrease in volume resistivity and breakdown voltage indicated that the filler agglomeration formed conductive pathways, which damaged the insulation performance. At the same time, in the aging resistance test, the decrease in tensile retention rate after UV aging and elongation retention rate after thermo-oxidative aging was related to the weakening of the UV shielding effect after the agglomeration of nanoparticles. Moreover, the cable's water resistance change rate was relatively high, further reflecting that the interfacial defects made it easier for water to penetrate. Therefore, silane coupling agent modification plays a decisive role in the uniform dispersion and interfacial strengthening of nano-zinc oxide, and its absence directly weakens the comprehensive performance of the main insulation layer.

[0281] As can be seen from the data of Comparative Example 14, when no transition layer was set between the outer protective layer and the main insulation layer, the performance problems of Comparative Example 14 were concentrated in interlayer bonding and weather resistance. The tensile strength and elongation at break of the cable prepared by Comparative Example 14 were significantly lower than those of Example 3, indicating that the polarity difference between the polyolefin outer protective layer and the silicone rubber main insulation layer caused stress concentration at the interface, which easily led to interlayer delamination. In terms of electrical performance, the decrease in breakdown voltage and volume resistivity was related to partial discharge caused by interface defects. At the same time, the aging resistance was particularly deteriorated. The tensile retention rate after ultraviolet aging was only 64.7%, and the elongation retention rate after thermo-oxidative aging was 63.1%, indicating that the lack of a transition layer in the "defense-in-depth" system allowed ultraviolet rays to penetrate directly to the main insulation layer, accelerating material degradation. The high value of the water resistance change rate further reflects the intensified water penetration at the interface. Therefore, the lack of a gradient transition layer not only weakened the interlayer bonding force, but also led to a significant reduction in the overall weather resistance of the cable.

[0282] As can be seen from the data of Comparative Example 15, when the UV absorber in the transition layer of Comparative Example 15 was not gradient blended, its performance defects were reflected in the continuity of UV protection and the interlayer stress distribution. Although its mechanical properties were better than those of Comparative Example 14, they were still lower than those of Example 3, indicating that a uniform low concentration of UV absorber could not effectively alleviate the sudden change in interlayer modulus. In terms of electrical performance, the decrease in breakdown voltage and volume resistivity was related to the increase in interfacial microcracks. In addition, in the aging resistance test, the decrease in tensile retention rate after UV aging and elongation retention rate after thermo-oxidative aging indicated that a single concentration of UV absorber could not form gradient protection, resulting in insufficient protection of the main insulation layer. The high rate of change in water resistance further indicated that the interfacial protection was incomplete. It can be seen that gradient blending design is indispensable for achieving multi-layer synergistic protection and smooth stress transition.

[0283] As can be seen from the data of Comparative Example 16, when titanium dioxide nanoparticles were not added to the self-cleaning layer, its performance shortcomings were concentrated in surface protection and dirt resistance. The contact angle of the cable prepared at this time was only 118°, which was much lower than 158° in Example 3. This indicates that the surface lacking the photocatalytic effect of titanium dioxide is prone to adsorbing pollutants, resulting in loss of hydrophobicity. Although its mechanical and electrical properties are close to those of Example 3, the decrease in tensile retention rate after ultraviolet aging and elongation retention rate after thermo-oxidative aging indicates that the accumulation of surface pollutants may accelerate the aging of the material. In addition, although the rate of change in water resistance is low, the deposition of dirt during long-term use may still cause partial discharge. Therefore, titanium dioxide modification plays a key role in maintaining the cleanliness of the cable surface, delaying aging, and preventing dirt flashover.

[0284] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An age resistant aerial insulated electrical cable, characterized in that, The cable comprises a conductor, an insulation layer and an outer sheath. The insulation layer is composed of a three-layer structure, from inside to outside, an inner shielding layer, a main insulation layer and an outer protective layer. The inner shielding layer is made of carbon black modified cross-linked polyethylene, and the thickness is 0.5-1.2mm. The main insulation layer is a nano zinc oxide-silicone rubber composite material, and 5-8wt% of nano zinc oxide particles are dispersed in the silicone rubber, and the thickness of the main insulation layer is 2-3.5mm. The outer protective layer is made of polyolefin modified by ultraviolet absorber, the ultraviolet absorber is benzotriazole compound, the content of benzotriazole compound is 1.5-3wt%, and the thickness of the outer protective layer is 0.8-1.5mm. The ultraviolet absorber of the outer protective layer is 2-(2'-hydroxy-5'-methylphenyl) benzotriazole; a transition layer is provided between the outer protective layer and the main insulation layer, the transition layer is a gradient blend of ultraviolet absorber and silicone rubber, and the content of ultraviolet absorber in the transition layer increases from 0.5wt% to 3wt% from inside to outside.

2. The age-resistant aerial insulated cable according to claim 1, characterized in that, The nano zinc oxide particles have a particle size of 20-50nm, and the surface of the nano zinc oxide is modified by a silane coupling agent.

3. The age-resistant aerial insulated cable of claim 1, wherein, The outer sheath is a three-layer structure, from inside to outside, a water-blocking non-woven fabric, a self-cleaning layer and an anti-aging polyvinyl chloride layer.

4. The age-resistant aerial insulated cable according to claim 3, characterized in that, The self-cleaning layer is a titanium dioxide nanoparticle modified polyurethane, the content of titanium dioxide is 2-5wt%, and the titanium dioxide is treated by ultraviolet light activation.

5. The age-resistant aerial insulated cable of claim 3, wherein, The anti-aging polyvinyl chloride layer contains 0.5-1.2wt% of antioxidant and 1-3wt% of hindered amine light stabilizer.

6. The age-resistant aerial insulated cable of claim 1, wherein, The conductor is a tight round aluminum conductor, and the surface of the tight round aluminum conductor is coated with a graphene coating layer with a thickness of 0.05-0.1mm.

7. The age-resistant aerial insulated cable according to claim 6, characterized in that, The graphene coating layer also embeds nano silver particles, the particle size of the nano silver particles is 10-30nm, and the content of nano silver is 5-15% of the mass of graphene. The graphene coating layer also embeds nano silver particles, the particle size of the nano silver particles is 10-30nm, and the content of nano silver is 5-15% of the mass of graphene.

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