Thermally aged crosslinked polyethylene insulated power cable and method of manufacture

Abstract

This invention relates to the field of power cable technology, specifically to a heat-resistant cross-linked polyethylene insulated power cable and its preparation method; from the inside out, it comprises a conductor core, an insulation layer, a filler layer, a composite functional layer, a steel tape armor layer, and a sheath layer; the insulation layer is composed of semi-conductive cross-linked polyethylene, silicone resin, nano-montmorillonite, and HALS light stabilizer; the filler layer is composed of plasticized fiberglass cloth, polyphenylene sulfide, and rare earth oxides; the composite functional layer, from the inside out, comprises a thermally conductive inner layer, a flame-retardant intermediate layer, and a UV-resistant outer layer; the sheath layer is composed of polyolefin, silica, ceramicized silicone rubber, flame retardant, polyethylene wax, and an initiator; this cable, by preferentially using cross-linked polyethylene and silicone resin as heat-resistant materials, provides multi-layer synergistic protection through thermal conductivity, flame retardancy, UV resistance, and armor, improving mechanical barrier performance while reducing thermal stress damage to internal materials, achieving a comprehensive improvement in heat aging resistance, and is suitable for harsh environments with high temperature, high humidity, and frequent thermal cycling.

Description

Technical Field

[0001] This invention relates to the field of power cable technology, specifically to a heat-resistant cross-linked polyethylene insulated power cable and its preparation method. Background Technology

[0002] Cross-linked polyethylene (XLPE) is a polymer commonly used in power cable insulation. Its main advantages are excellent electrical properties and heat resistance, maintaining good insulation performance under high temperature and high pressure. XLPE insulated power cables are manufactured using chemical or physical methods to transform the linear molecular structure of polyethylene into a three-dimensional network structure, changing it from thermoplastic polyethylene to thermosetting cross-linked polyethylene. This improves the aging resistance, mechanical properties, and environmental resistance of polyethylene while maintaining excellent electrical properties. Furthermore, it offers advantages such as light weight, simple structure, ease of use, resistance to chemical corrosion, and unrestricted installation regardless of elevation differences.

[0003] However, when cross-linked polyethylene is exposed to high temperatures (>90℃) for a long time, the CH and CC bonds in the molecular chain will break due to thermal oxidation, which will cause the three-dimensional cross-linked network to gradually disintegrate, resulting in a decrease in mechanical strength and insulation performance. In a humid and hot environment, moisture penetration accelerates the hydrolysis reaction of the material, destroys the cross-linked structure, and further reduces thermal stability. Frequent thermal cycling will also cause the material to repeatedly shrink and expand, leading to fatigue crack propagation and interfacial adhesion failure. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a heat-resistant cross-linked polyethylene insulated power cable, comprising, from the inside out, a conductor core, an insulation layer, a filler layer, a composite functional layer, a steel tape armor layer, and a sheath layer.

[0005] The insulating layer is composed of semi-conductive cross-linked polyethylene, silicone resin, nano-montmorillonite, and HALS light stabilizer in a mass ratio of 1:0.2-0.3:0.2-0.4:0.08-0.1.

[0006] The filling layer is composed of plasticized fiberglass cloth, polyphenylene sulfide, and rare earth oxides in a mass ratio of 1:0.3-0.5:0.05-0.08;

[0007] The composite functional layer comprises, from the inside out, a thermally conductive inner layer, a flame-retardant intermediate layer, and a UV-resistant outer layer, with a layer thickness ratio of 0.1–0.3: 0.2–0.4: 0.05–0.1.

[0008] The sheath layer, by weight, consists of 25-35 parts polyolefin, 9-12 parts silica, 10-15 parts ceramicized silicone rubber, 10-15 parts flame retardant, 1-3 parts polyethylene wax, and 0.02-0.04 parts initiator.

[0009] Explanation: On the conductor surface covered by the semi-conductive tape, the thermally stable plasticizer silicone resin prevents softening at high temperatures; the semi-conductive cross-linked polyethylene reduces partial discharge and improves voltage withstand capability; the polyethylene itself has good heat resistance; nano-montmorillonite, as a filler, increases the material's mechanical strength and barrier properties, delaying thermal aging; HALS light stabilizer is used to capture free radicals and prevent UV- or heat-induced oxidative degradation. This combination of materials significantly enhances the insulation layer's resistance to thermal aging. The plasticized fiberglass cloth itself is heat-resistant; the addition of polyphenylene sulfide improves the heat resistance and flame retardancy of the filler layer; rare earth oxides, as stabilizers, help the material remain stable at high temperatures and delay aging. Such a filler layer may not only resist thermal aging but also improve mechanical strength and flame retardancy; the thermally conductive layer may help dissipate heat, reduce the internal temperature of the cable, and reduce thermal aging; the flame-retardant layer improves fire resistance; and the UV-resistant layer prevents UV degradation, making it suitable for outdoor environments. This three-layer design comprehensively enhances the cable's environmental adaptability and long-term stability. Polyolefin itself is resistant to chemical corrosion, silica acts as a reinforcing agent, and ceramicized silicone rubber forms a ceramic protective layer at high temperatures, improving fire resistance. The flame retardant decomposes and absorbs heat, inhibiting combustion. Polyethylene wax improves processing performance, and an initiator is used for the cross-linking reaction. This sheath exhibits excellent flame retardancy, high-temperature resistance, and mechanical protection.

[0010] Furthermore, the thickness ratio of the insulating layer, filling layer, composite functional layer, steel strip armor layer, and sheath layer is 1:1:1.5~2.5:1:2~3;

[0011] Note: The cables obtained with the above thickness ratio have more stable structure and environmental adaptability.

[0012] Furthermore, the method for preparing the composite functional layer is as follows:

[0013] S1-1. Using polyolefin as the base material, a thermally conductive filler accounting for 15-25% of the mass of the polyolefin is added. The base material and the thermally conductive filler are melt-blended at a temperature of 180-200°C using a twin-screw extruder. The shear rate is controlled at 300-600 rpm to uniformly disperse the filler. The thermally conductive inner layer is obtained by blown film molding. The thermally conductive filler is composed of boron nitride and silane coupling agent in a ratio of 1:0.5-0.8.

[0014] S1-2. Using ethylene-vinyl acetate as the matrix, add 30-40% flame retardant by mass of the ethylene-vinyl acetate, dry at 95-105°C for 3.5-4.5 hours, and then extrude at 200-220°C to obtain a flame retardant intermediate layer.

[0015] S1-3. Using thermoplastic polyurethane as the base material, 5-8% of modified nano-TiO2 and 2-3% of silicone masterbatch are added to the thermoplastic polyurethane. The mixture is extruded at a temperature of 200-220°C to obtain an anti-UV outer layer. After surface treatment, the outer layer is compounded with a flame-retardant intermediate layer and a thermally conductive inner layer in sequence through a hot press roller under a pressure of 0.5-1.0 MPa and a temperature of 25-180°C to obtain a composite functional layer.

[0016] Description: The composite functional layer significantly improves heat aging resistance through a synergistic design of thermal conductivity, flame retardancy, and UV resistance, along with optimized interfacial chemical bonding. Boron nitride rapidly dissipates heat, preventing localized temperature rises that could lead to substrate thermal decomposition. Silane coupling agents enhance the interfacial bonding between boron nitride and polyolefins, inhibiting stress cracking caused by filler shedding at high temperatures. Silicone masterbatch improves the outer layer's weather resistance and resistance to damp heat aging, improves the melt flowability of thermoplastic polyurethane, and reduces molecular chain breakage caused by processing heat history. Silane coupling agents surface-modify the thermally conductive filler, reducing the interfacial thermal resistance between the filler and substrate, while also inhibiting interlayer delamination caused by damp heat aging. Under long-term thermal aging or damp heat cycling at 150℃, the mechanical property retention rate is ≥85%, meeting the requirements of harsh environmental applications.

[0017] Furthermore, the flame retardant is composed of aluminum hydroxide and zinc borate compounded in a mass ratio of 2 to 3:1;

[0018] Note: The combination of aluminum hydroxide and zinc borate enhances the high-temperature stability of the flame-retardant layer through a catalytic char formation mechanism, thereby achieving a flame-retardant effect.

[0019] Furthermore, in S1-3, the method for preparing the modified nano-TiO2 is as follows:

[0020] The nano-TiO2 was divided into 2 to 3 parts. One part was ultrasonically dispersed in ethanol with a silane coupling agent at a mass ratio of 1:0.3 for 30 min. After drying, the first modified TiO2 was obtained.

[0021] Take the remaining 1-2 parts of nano-TiO2, 5-8% of mica tape by weight of the nano-TiO2, and 0.5-2% of aminosilane by weight of the nano-TiO2, and perform plasma treatment at a power of 45-50W for 50-60s to obtain the second modified TiO2; mix the first modified TiO2 and the second modified TiO2 at a ratio of 1:1 to obtain modified nano-TiO2;

[0022] Explanation: The methacryloyloxy group of the silane coupling agent KH-570 combines with the hydroxyl groups on the surface of nano-TiO2 through hydrolysis, forming a hydrophobic organic layer, reducing agglomeration and enhancing compatibility with thermoplastic polyurethane. Ethanol ultrasonic dispersion further ensures uniform filler distribution, avoiding localized agglomeration that leads to decreased light scattering efficiency. The amino functional groups of the aminosilane combine with nano-TiO2 and mica tape through plasma activation, forming a chemically bonded network. Simultaneously, the mica tape acts as a sheet-like support, inhibiting filler sedimentation. The first modified TiO2 scatters ultraviolet light through its high refractive index, while the second modified TiO2 enhances photocatalytic passivation capabilities through plasma-activated surface defects. After mixing, a broad-spectrum UV shielding layer is formed. The hydrophobicity of KH-570 and the amino crosslinking effect of the aminosilane KH-550 synergistically reduce the degradation of thermoplastic polyurethane in humid and hot environments (85℃ / 85%). The molecular chain is hydrolyzed under RH to maintain long-term UV resistance. The stepwise modification strategy achieves efficient functionalization of nano-TiO2 in thermoplastic polyurethane substrate through chemical bonding optimization and physical structure regulation, providing high-reliability UV resistance and interface stability for multilayer composite structures. The rigidity enhancement of the first modified TiO2 and the flexible interface buffer of the second modified TiO2 are combined to make the tensile strength of the outer layer of thermoplastic polyurethane ≥25MPa and the elongation at break ≥400%.

[0023] Further, in S1-3, the surface treatment method is as follows: ultraviolet irradiation treatment is performed between each layer, with an irradiation wavelength of 254-365 nm and an irradiation intensity of 50-100 mW / cm². 2 Processing time: 30–120 seconds;

[0024] Explanation: UV light is used to induce the generation of free radicals on the TPU surface, which promotes chemical bonding with the EVA flame-retardant layer.

[0025] Furthermore, in S1-3, the UV-resistant outer layer and the flame-retardant intermediate layer, as well as the flame-retardant intermediate layer and the heat-conducting inner layer, are all composited using a segmented composite process during the hot press roller bonding process.

[0026] First stage: Pressurize at 0.5MPa and 180℃ for 15-30s, then add 1-3wt% of epoxy-modified silicone resin to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer, and apply microwave-ultrasonic composite field treatment for 10-20s, wherein the microwave power is 200-500W and the ultrasonic frequency is 20-40kHz.

[0027] The second stage: pressurize at 1.0 MPa and 120°C for 15-30 seconds. During the pressurization process, add 1-2 wt% of nano-silver antibacterial agent to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer. Then apply microwave-ultrasound composite field treatment for 15-25 seconds, where the microwave power is 100-300W and the ultrasonic frequency is 15-30kHz.

[0028] The third stage: pressurize at 0.8 MPa and 25-30℃, and hold the pressure for 30-60 seconds.

[0029] Explanation: In the first stage of high-temperature interfacial bonding, microwave treatment reduces the curing time of epoxy resin by 30-50% compared to traditional heating, while ultrasound can eliminate interfacial micropores and increase peel strength by 15-20%. In the second stage of antibacterial agent dispersion, the ultrasonic cavitation effect makes the average particle size of nano-silver ≤50nm, which inhibits the aggregation of nano-silver. Furthermore, microwave treatment can improve the uniformity of nano-silver distribution and eliminate local enrichment, further increasing the antibacterial rate to ≥99.9%. Finally, the extended holding time in the low-temperature stage can release residual stress and ensure the stability of the interlayer structure.

[0030] This invention also provides a method for preparing a heat-resistant cross-linked polyethylene insulated power cable, comprising the following steps:

[0031] S1. Take 3 to 5 copper wires and twist them together to obtain 2 to 4 sets of conductor cores. Then, mix, stir, defoam, extrude and coat the semi-conductive cross-linked polyethylene, silicone resin, nano montmorillonite and HALS light stabilizer onto the surface of the conductor cores to obtain an insulation layer.

[0032] S2. Then, the conductor cores with insulation layers in each group are twisted together, and the plasticized fiberglass cloth, polyphenylene sulfide and rare earth oxides are mixed, defoamed, extruded and filled into the gaps of the twisted conductor cores to obtain a filling layer.

[0033] S3. Apply an adhesive to the outside of the insulation layer and the filling layer and bond it to the composite functional layer. Wrap two layers of aluminum-plated steel strip around the composite functional layer to obtain the steel strip armor layer. Finally, wrap the sheath layer around the steel strip armor layer to obtain the power cable.

[0034] Description: Multiple copper wires are twisted together to form a conductor core. Plasticized fiberglass cloth is used to fill the gaps between the twisted conductors to improve the distribution of mechanical stress. Semi-conductive cross-linked polyethylene forms a three-dimensional network structure through a cross-linking process, which significantly improves thermal stability. The nano-montmorillonite layer structure hinders oxygen diffusion paths and reduces the oxidation rate of the insulation layer. The rare earth oxide is cerium oxide, which can catalyze the decomposition of peroxides and inhibit the accumulation of high-temperature oxidation byproducts.

[0035] Furthermore, the adhesive is a silicone rubber-based adhesive;

[0036] Note: Silicone rubber-based adhesives have good temperature and weather resistance, as well as good flexibility and electrical insulation properties.

[0037] Furthermore, the initiator is dicumyl peroxide or bis(2,5-diphenyl)oxide;

[0038] Note: Dicumyl peroxide decomposes at high temperatures to generate free radicals, which initiate cross-linking of polyolefins and promote the vulcanization of silicone rubber. Dicumyl peroxide can reduce the risk of thermal degradation of polyolefins and has good compatibility with polyethylene wax lubricants.

[0039] Compared with existing technologies, the beneficial effects of this invention are:

[0040] (1) The power cable prepared by the present invention uses cross-linked polyethylene and silicone resin as heat-resistant materials, and provides multi-layer synergistic protection of thermal conductivity, flame retardancy, UV resistance and armor. The thermally conductive inner layer quickly dissipates Joule heat from the conductor, avoiding local temperature rise and accelerated thermal aging; the flame-retardant middle layer delays heat transfer by absorbing heat and decomposing, and inhibits high-temperature combustion; the aluminized steel strip armor layer reflects external radiant heat, and the double-layer wrapping structure improves the mechanical barrier performance and reduces thermal stress damage to the internal materials; thus achieving a comprehensive improvement in heat aging resistance, it is suitable for harsh environments with high temperature, high humidity and frequent thermal cycling.

[0041] (2) In this invention, TiO2 is divided into two parts and treated with different coupling agents and plasma treatments. The first part is treated with a silane coupling agent, and the second part is treated with an aminosilane and plasma treatment. After mixing, it is used in the UV-resistant layer of thermoplastic polyurethane. The silane coupling agent can provide compatibility with thermoplastic polyurethane, while the amino group of the aminosilane can form a stronger physical bond with the flame-retardant intermediate layer after plasma treatment, realizing the efficient functionalization of nano-TiO2 in TPU substrate, providing high reliability of UV resistance and interface stability for multilayer composite structures. The rigidity enhancement of the first modified TiO2 and the flexible interface buffer of the second modified TiO2 are combined to enhance the tensile strength and elongation at break of the outer layer of thermoplastic polyurethane, thereby optimizing the performance of power cables. Attached Figure Description

[0042] Figure 1 This is a comparison chart of the heat aging resistance of cross-linked polyethylene insulated power cables of Examples 1 to 11 and Control Groups 1 to 2 of the present invention;

[0043] Figure 2 This is a comparison diagram of the tensile strength of cross-linked polyethylene insulated power cables in Examples 1 to 11 and Control Groups 1 to 2 of the present invention;

[0044] Figure 3This is a comparison chart of the peel strength retention rate of cross-linked polyethylene insulated power cables in Examples 1 to 11 and Control Groups 1 to 2 of the present invention;

[0045] Figure 4 This is a comparison chart of the heat aging resistance of cross-linked polyethylene insulated power cables in Examples 1, 11 to 15, and Control Groups 3 to 4 of the present invention;

[0046] Figure 5 This is a comparison chart of the tensile strength of cross-linked polyethylene insulated power cables in Embodiments 1, 11 to 15, and Control Groups 3 to 4 of the present invention;

[0047] Figure 6 This is a comparison chart of the peel strength retention rate of cross-linked polyethylene insulated power cables in Examples 1, 11 to 15 and Control Groups 3 to 4 of the present invention;

[0048] Figure 7 This is a comparison chart of the heat aging resistance of cross-linked polyethylene insulated power cables in Embodiments 1, 16 to 22 of the present invention;

[0049] Figure 8 This is a comparison diagram of the tensile strength of cross-linked polyethylene insulated power cables in Embodiments 1, 16 to 22 of the present invention;

[0050] Figure 9 This is a comparison chart of the peel strength retention rate of cross-linked polyethylene insulated power cables in Examples 1, 16 to 22 of the present invention. Detailed Implementation

[0051] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0052] Example 1: A heat-resistant cross-linked polyethylene insulated power cable, comprising, from the inside out, a conductor core, an insulation layer, a filler layer, a composite functional layer, a steel tape armor layer, and a sheath layer;

[0053] The insulating layer is composed of semi-conductive cross-linked polyethylene, silicone resin, nano-montmorillonite, and HALS light stabilizer in a mass ratio of 1:0.25:0.3:0.09;

[0054] The filling layer is composed of plasticized fiberglass cloth, polyphenylene sulfide, and rare earth oxides in a mass ratio of 1:0.4:0.06; the rare earth oxide is cerium oxide.

[0055] The composite functional layer consists of a thermally conductive inner layer, a flame-retardant intermediate layer, and a UV-resistant outer layer, from the inside out, with a layer thickness ratio of 0.2:0.3:0.07.

[0056] The sheath layer, by weight, consists of 30 parts polyolefin, 10 parts silica, 13 parts ceramicized silicone rubber, 13 parts flame retardant, 2 parts polyethylene wax, and 0.03 parts initiator; the initiator is dicumyl peroxide.

[0057] The thickness ratio of the insulation layer, filling layer, composite functional layer, steel strip armor layer, and sheath layer is 1:1:2:1:2.5;

[0058] The method for preparing the composite functional layer is as follows:

[0059] S1-1. Using polyolefin as the base material, add 20% thermally conductive filler by mass of polyolefin. Melt-blend the base material and thermally conductive filler at 190℃ using a twin-screw extruder. Control the shear rate at 450rpm to uniformly disperse the filler. Form the thermally conductive inner layer by blown film method. The thermally conductive filler is composed of boron nitride and silane coupling agent in a ratio of 1:0.7.

[0060] S1-2. Using ethylene-vinyl acetate as the matrix, a flame retardant of 35% by mass of ethylene-vinyl acetate is added. After drying at 411℃ for 4 hours, the mixture is extruded at 210℃ to obtain a flame retardant intermediate layer. The flame retardant is composed of aluminum hydroxide and zinc borate compounded in a mass ratio of 2.5:1.

[0061] S1-3. Using thermoplastic polyurethane as the base material, 7% modified nano-TiO2 (by mass of thermoplastic polyurethane) and 2.5% silicone masterbatch (by mass of thermoplastic polyurethane) are added. The mixture is extruded at 210℃ to obtain a UV-resistant outer layer. After surface treatment, it is sequentially laminated with a flame-retardant intermediate layer and a thermally conductive inner layer through a hot press roller under a pressure of 0.8MPa and a temperature of 150℃ to obtain a composite functional layer. The surface treatment method is: ultraviolet irradiation treatment is applied between each layer at a wavelength of 288nm and an irradiation intensity of 75mW / cm². 2 The processing time was 80 seconds. In this embodiment, the modified nano-TiO2 was obtained by mixing it with a silane coupling agent at a mass ratio of 1:0.3 and then dispersing it in 95% ethanol at a volume ratio of 1:8.

[0062] A method for preparing a heat-resistant cross-linked polyethylene insulated power cable includes the following steps:

[0063] S1. Take four copper wires and twist them together to obtain three sets of conductor cores. Then, mix, stir, defoam, extrude and coat the semi-conductive cross-linked polyethylene, silicone resin, nano montmorillonite and HALS light stabilizer on the surface of the conductor cores to obtain an insulation layer.

[0064] S2. Then, the conductor cores with insulation layers in each group are twisted together, and the plasticized fiberglass cloth, polyphenylene sulfide and rare earth oxides are mixed, defoamed, extruded and filled into the gaps of the twisted conductor cores to obtain a filling layer.

[0065] S3. Apply a silicone rubber-based adhesive to the outside of the insulation layer and the filling layer and bond it to the composite functional layer. Wrap two layers of aluminum-plated steel tape around the composite functional layer to obtain the steel tape armor layer. Finally, wrap the sheath layer around the steel tape armor layer to obtain the power cable.

[0066] Example 2: Unlike Example 1, the insulating layer is composed of semi-conductive cross-linked polyethylene, silicone resin, nano-montmorillonite and HALS light stabilizer in a mass ratio of 1:0.2:0.2:0.08.

[0067] Example 3: Unlike Example 1, the insulating layer is composed of semi-conductive cross-linked polyethylene, silicone resin, nano-montmorillonite and HALS light stabilizer in a mass ratio of 1:0.3:0.4:0.1.

[0068] Example 4: Unlike Example 1, the filling layer is composed of plasticized fiberglass cloth, polyphenylene sulfide and rare earth oxides in a mass ratio of 1:0.3:0.05.

[0069] Example 5: Unlike Example 1, the filler layer is composed of plasticized fiberglass cloth, polyphenylene sulfide and rare earth oxides in a mass ratio of 1:0.5:0.08.

[0070] Example 6: Unlike Example 1, the interlayer thickness ratio is 0.1:0.2:0.05.

[0071] Example 7: Unlike Example 1, the interlayer thickness ratio is 0.3:0.4:0.1.

[0072] Example 8: Unlike Example 1, the sheath layer is composed of 25 parts polyolefin, 9 parts silica, 10 parts ceramicized silicone rubber, 10 parts flame retardant, 1 part polyethylene wax and 0.02 parts initiator by weight.

[0073] Example 9: Unlike Example 1, the sheath layer is composed of 35 parts polyolefin, 12 parts silica, 15 parts ceramicized silicone rubber, 15 parts flame retardant, 3 parts polyethylene wax and 0.04 parts initiator by weight.

[0074] Example 10: Unlike Example 1, the thickness ratio of the insulation layer, filling layer, composite functional layer, steel tape armor layer and sheath layer is 1:1:1.5:1:2.

[0075] Example 11: Unlike Example 1, the thickness ratio of the insulation layer, filling layer, composite functional layer, steel tape armor layer and sheath layer is 1:1:2.5:1:3.

[0076] Example 12: Unlike Example 1, the method for preparing the composite functional layer is as follows:

[0077] S1-1. Using polyolefin as the base material, add 15% thermally conductive filler by mass of polyolefin. Melt-blend the base material and thermally conductive filler at 180℃ using a twin-screw extruder. Control the shear rate at 300rpm to uniformly disperse the filler. Form the thermally conductive inner layer by blown film method. The thermally conductive filler is composed of boron nitride and silane coupling agent in a ratio of 1:0.5.

[0078] S1-2. Using ethylene-vinyl acetate as the matrix, add 30% flame retardant by mass of ethylene-vinyl acetate, dry at 95°C for 3.5 h, and then extrude at 200°C to obtain a flame retardant intermediate layer.

[0079] S1-3. Using thermoplastic polyurethane as the base material, 5% modified nano-TiO2 and 2% silicone masterbatch by mass of thermoplastic polyurethane are added. The mixture is extruded at 200℃ to obtain a UV-resistant outer layer. After surface treatment, it is sequentially laminated with a flame-retardant intermediate layer and a thermally conductive inner layer through a hot press roller under a pressure of 0.5MPa and a temperature of 25℃ to obtain a composite functional layer. The surface treatment method is as follows: ultraviolet irradiation treatment is applied between each layer at a wavelength of 254nm and an irradiation intensity of 50mW / cm². 2 Processing time: 30 seconds.

[0080] Example 13: Unlike Example 1, the method for preparing the composite functional layer is as follows:

[0081] S1-1. Using polyolefin as the base material, add 25% thermally conductive filler by mass of polyolefin. Melt-blend the base material and thermally conductive filler at 200℃ using a twin-screw extruder. Control the shear rate at 600rpm to uniformly disperse the filler. Form the thermally conductive inner layer by blown film method. The thermally conductive filler is composed of boron nitride and silane coupling agent in a ratio of 1:0.8.

[0082] S1-2. Using ethylene-vinyl acetate as the matrix, add 40% flame retardant by mass of ethylene-vinyl acetate, dry at 105℃ for 4.5h and then extrude at 220℃ to obtain a flame retardant intermediate layer.

[0083] S1-3. Using thermoplastic polyurethane as the base material, 8% modified nano-TiO2 and 3% silicone masterbatch by mass of thermoplastic polyurethane are added. The mixture is extruded at 220℃ to obtain a UV-resistant outer layer. After surface treatment, it is sequentially laminated with a flame-retardant intermediate layer and a thermally conductive inner layer through a hot press roller under a pressure of 1.0 MPa and a temperature of 180℃ to obtain a composite functional layer. The surface treatment method is as follows: ultraviolet irradiation treatment is applied between each layer at a wavelength of 365 nm and an irradiation intensity of 100 mW / cm². 2 Processing time: 120 seconds.

[0084] Example 14: Unlike Example 1, in S1-2, the flame retardant is composed of aluminum hydroxide and zinc borate compounded in a mass ratio of 2:1.

[0085] Example 15: Unlike Example 1, in S1-2, the flame retardant is composed of aluminum hydroxide and zinc borate compounded in a mass ratio of 3:1.

[0086] Example 16: Unlike Example 1, in S1-3, the preparation method of modified nano-TiO2 is as follows:

[0087] Nano TiO2 was divided into two equal parts. One part was mixed with a silane coupling agent at a mass ratio of 1:0.3. Then, it was added to 95% ethanol at a ratio of 1g:8mL and ultrasonically dispersed for 30min. After drying, the first modified TiO2 was obtained.

[0088] The remaining 1 part of nano-TiO2, 7% of the weight of nano-TiO2 mica tape and 1.2% of the weight of nano-TiO2 aminosilane were subjected to plasma treatment at a power of 48W for 55s to obtain the second modified TiO2. The first modified TiO2 and the second modified TiO2 were mixed in a 1:1 ratio to obtain modified nano-TiO2.

[0089] Example 17: Unlike Example 16, in S1-3, the preparation method of modified nano-TiO2 is as follows:

[0090] Nano TiO2 was divided into two equal parts. One part was mixed with a silane coupling agent at a mass ratio of 1:0.3. Then, it was added to 95% ethanol at a ratio of 1g:5mL and ultrasonically dispersed for 30min. After drying, the first modified TiO2 was obtained.

[0091] The remaining 1 part of nano-TiO2, 5% of the weight of nano-TiO2 mica tape and 0.5% of the weight of nano-TiO2 aminosilane were subjected to plasma treatment at a power of 45W for 50s to obtain the second modified TiO2. The first modified TiO2 and the second modified TiO2 were mixed in a 1:1 ratio to obtain modified nano-TiO2.

[0092] Example 18: Unlike Example 16, in S1-3, the preparation method of modified nano-TiO2 is as follows:

[0093] Nano TiO2 was divided into 3 equal parts. One part was mixed with silane coupling agent at a mass ratio of 1:0.3. Then, it was added to 95% ethanol at a ratio of 1g:10mL and ultrasonically dispersed for 30min. After drying, the first modified TiO2 was obtained.

[0094] The remaining two parts of nano-TiO2, 8% of the weight of nano-TiO2 mica tape, and 2% of the weight of nano-TiO2 aminosilane were subjected to plasma treatment at a power of 50W for 60s to obtain the second modified TiO2. The first modified TiO2 and the second modified TiO2 were mixed in a 1:1 ratio to obtain modified nano-TiO2.

[0095] Example 19: Unlike Example 16, in S1-3, the UV-resistant outer layer and flame-retardant intermediate layer, and the flame-retardant intermediate layer and thermally conductive inner layer are all composited using a segmented composite process in the hot press roller process.

[0096] First stage: Pressurize at 0.5MPa and 180℃ for 22s, then add 3wt% epoxy-modified silicone resin to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer, and apply microwave-ultrasonic composite field treatment for 15s, where the microwave power is 350W and the ultrasonic frequency is 30kHz.

[0097] The second stage: pressurize at 1.0 MPa and 120℃ for 22 seconds. During the pressurization process, add 1.5 wt% nano-silver antibacterial agent to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer. Then apply microwave-ultrasound composite field treatment for 20 seconds, with microwave power of 200W and ultrasonic frequency of 22kHz.

[0098] The third stage: pressurize at 0.8 MPa and 25-30℃, and hold the pressure for 45 seconds.

[0099] Example 20: Unlike Example 19, in S1-3, the UV-resistant outer layer and flame-retardant intermediate layer, and the flame-retardant intermediate layer and thermally conductive inner layer are all composited using a segmented composite process in the hot press roller process.

[0100] First stage: Pressurize at 0.5MPa and 180℃ for 15s, then add 1wt% epoxy-modified silicone resin to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer, and apply microwave-ultrasonic composite field treatment for 10s, where the microwave power is 200W and the ultrasonic frequency is 20kHz.

[0101] The second stage: pressurize at 1.0 MPa and 120℃ for 15 seconds. During the pressurization process, add 1 wt% of nano-silver antibacterial agent to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer. Then apply microwave-ultrasound composite field treatment for 15 seconds, with microwave power of 100W and ultrasonic frequency of 15kHz.

[0102] The third stage: pressurize at 0.8 MPa and 25°C, and hold the pressure for 30 seconds.

[0103] Example 21: Unlike Example 19, in S1-3, the UV-resistant outer layer and flame-retardant intermediate layer, and the flame-retardant intermediate layer and thermally conductive inner layer are all composited using a segmented composite process in the hot press roller process.

[0104] First stage: Pressurize at 0.5MPa and 180℃ for 30s, then add 3wt% epoxy-modified silicone resin to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer, and apply microwave-ultrasonic composite field treatment for 20s, where the microwave power is 500W and the ultrasonic frequency is 40kHz.

[0105] The second stage: pressurize at 1.0MPa and 120℃ for 30s. During the pressurization process, add 2wt% of nano-silver antibacterial agent to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer. Then apply microwave-ultrasound composite field treatment for 25s, with microwave power of 300W and ultrasonic frequency of 30kHz.

[0106] The third stage: pressurize at 0.8 MPa and 30°C, and hold the pressure for 60 seconds.

[0107] Example 22: Unlike Example 19, the initiator is bis(2,5)-5.

[0108] Experimental Example: This experimental example is based on the scheme described in Example 1, aiming to illustrate the practical application effect of the present invention. The power cables obtained from each example were tested for heat aging resistance, tensile strength, and damp heat cycling. The average of three test results for each example was taken as the final test result. The investigation is as follows:

[0109] Performance tests were conducted on the power cables obtained in Examples 1-22 respectively. Thermal stability time test: Test samples were prepared according to GB / T2951.11-2008 and placed on a clean glass plate. When the temperature of the thermal aging test chamber was raised to 200°C, the glass plate was quickly placed in it. Timing was started when the temperature reached 200°C. The color change was observed and the time required for the color to start to turn slightly yellow was recorded as the thermal stability time at 200°C.

[0110] The damp heat cycling test (-40℃~85℃ / 85% RH, 100 cycles) was used to verify the interlayer adhesion stability, i.e., the peel strength retention rate. The test results are as follows:

[0111] 1. Investigate the influence of component composition on the performance of cross-linked polyethylene insulated power cables.

[0112] Control group 1: Unlike Example 1, no silicone resin was added to the insulating layer.

[0113] Control group 2: Unlike Example 1, the filler layer does not contain rare earth oxides.

[0114] Conclusion: Comparison of Examples 1-3 and Control Group 1 shows that the absence of silicone resin reduces the heat aging resistance, tensile strength, and peel strength retention rate of the power cable. This is because the insulation layer lacking silicone resin decomposes more rapidly at temperatures above 90°C, reducing the elongation at break retention rate of cross-linked polyethylene from ≥80% to ≤60%. Simultaneously, HALS (Hyper-Hyper-Laminated Fiber) migrates and fails rapidly due to the lack of a fixed carrier, preventing effective repair of interfacial microcracks and thus reducing the thermal stability time. The toughening effect of silicone resin is lost, and the tensile strength retention rate of the insulation layer decreases with increasing heat aging time. Furthermore, nano-montmorillonite is prone to delamination due to insufficient interfacial bonding, leading to a decrease in tensile strength. Meanwhile, due to the high fluidity of silicone resin, it can penetrate into the interfacial microcracks of the composite material, thereby enhancing interlayer adhesion and increasing peel strength by approximately 20%.

[0115] The comparison of Examples 1, 4-5, and Control Group 2 shows that the absence of rare earth oxides also reduces the heat aging resistance, tensile strength, and peel strength retention rate of power cables. This is because rare earth oxides have a catalytic carbonization effect, which can improve the thermal stability of polyphenylene sulfide at a thermal decomposition temperature ≥200℃. When rare earth oxides are lacking, the thermal oxidation rate of the filler layer above 200℃ is accelerated, and the thermal stability time is shortened by ≥30%. Rare earth oxides can improve the interfacial compatibility between plasticized fiberglass cloth and polyphenylene sulfide. When they are missing, fiber and resin are prone to debonding inside the filler layer, and the tensile strength decreases by ≥15%. At the same time, rare earth oxides can inhibit the hydrolysis reaction of polyphenylene sulfide in a humid and hot environment. When they are missing, the peel strength retention rate of the interface between the filler layer and the adjacent layer decreases from ≥80% to ≤60% due to water absorption and swelling.

[0116] 2. Investigate the influence of the preparation method of the composite functional layer on the performance of cross-linked polyethylene insulated power cables.

[0117] Control Group 3: Unlike Example 1, the surface treatment was performed using plasma treatment with a power of 75W and a duration of 60s.

[0118] Control group 4: Unlike Example 1, no silicone masterbatch was added during the preparation of the UV-resistant outer layer.

[0119] Conclusion: Comparison of Examples 1, 12-15, and Control Groups 3 and 4 shows that plasma treatment instead of UV irradiation and the absence of silicone masterbatch during UV-resistant outer layer preparation both lead to a decrease in the performance of the composite functional layer. This is because high-intensity UV irradiation optimizes the dispersibility of nano-TiO2 and silicone masterbatch, improving the fiber-substrate interface shear strength. While plasma treatment increases surface roughness, it only forms a physical bond, resulting in a lower improvement in interface shear strength and susceptibility to failure due to humid and hot environments. UV light induces Si-O bonds in the silicone masterbatch to... The TPU substrate forms covalent bonds, and the peel strength retention rate after humid heat aging is ≥80%. Plasma treatment relies on physical adsorption, and the interface is prone to water absorption and expansion in humid heat environment, resulting in a significant decrease in peel strength retention rate. In the preparation of the UV-resistant outer layer, if silicone masterbatch is not added, the interface between TPU and flame-retardant intermediate layer will be loose due to the lack of silicone masterbatch, the oxygen permeability will increase, and the thermal stability time will decrease by ≥20%. Without silicone masterbatch, the uneven distribution of nanoparticles will cause microcracks, and the tensile strength will decrease by ≥18%. Without silicone masterbatch, the interface relies on physical adsorption, and the peel strength retention rate after humid heat aging decreases by ≥30%.

[0120] 3. Investigate the effect of modified nano-TiO2 and hot-pressing roller composite method on the performance of cross-linked polyethylene insulated power cables.

[0121] Conclusion: Comparison of Examples 1 and 16-18 shows that the preparation method of modified nano-TiO2 in this application has a positive impact on improving the performance of cross-linked polyethylene insulated power cables. Specifically, the first modified TiO2 modified with silane coupling agent forms a dense coating layer through the hydrophobic groups (such as -CH3) of the silane coupling agent, reducing moisture and oxygen penetration and inhibiting thermal oxidation decomposition of the substrate at high temperatures. In the second modified TiO2, the synergistic effect of mica tape and plasma treatment forms a multi-layer heat insulation structure in the cable insulation layer, delaying heat transfer and extending the thermal stability time. The lamellar structure of mica tape is combined with aminosilane through plasma treatment, and the tensile strength is improved after embedding into the substrate. The hydrophobicity of aminosilane and the layered structure of mica tape work synergistically to reduce the water absorption rate at the cable interface, and the peel strength retention rate after wet heat aging is also significantly improved.

[0122] A comparison of Examples 16 and 19 to 22 shows that segmented mixing can further improve the heat aging resistance, tensile strength and peel strength retention of cross-linked polyethylene insulated power cables. Considering all factors, Example 19 is the optimal solution.

Claims

1. A cross-linked polyethylene insulated power cable resistant to heat aging, characterized in that, From the inside out, it includes the conductor core, insulation layer, filler layer, composite functional layer, steel tape armor layer, and sheath layer; The insulating layer is composed of semi-conductive cross-linked polyethylene, silicone resin, nano-montmorillonite, and HALS light stabilizer in a mass ratio of 1:0.2~0.3:0.2~0.4:0.08~0.1; The filling layer is composed of plasticized fiberglass cloth, polyphenylene sulfide, and cerium oxide in a mass ratio of 1:0.3~0.5:0.05~0.08; The composite functional layer comprises, from the inside out, a thermally conductive inner layer, a flame-retardant intermediate layer, and a UV-resistant outer layer, with a layer thickness ratio of 0.1~0.3:0.2~0.4:0.05~0.

1. The sheath layer, by weight, consists of 25-35 parts polyolefin, 9-12 parts silica, 10-15 parts ceramicized silicone rubber, 10-15 parts flame retardant, 1-3 parts polyethylene wax, and 0.02-0.04 parts initiator.

2. The heat-resistant cross-linked polyethylene insulated power cable as described in claim 1, characterized in that, The thickness ratio of the insulation layer, filling layer, composite functional layer, steel strip armor layer and sheath layer is 1:1:1.5~2.5:1:2~3.

3. The heat-resistant cross-linked polyethylene insulated power cable as described in claim 2, characterized in that, The method for preparing the composite functional layer is as follows: S1-1. Using polyolefin as the base material, a thermally conductive filler accounting for 15-25% of the mass of the polyolefin is added. The base material and the thermally conductive filler are melt-blended at a temperature of 180-200℃ using a twin-screw extruder. The shear rate is controlled at 300-600 rpm to uniformly disperse the filler. The thermally conductive inner layer is obtained by blown film molding. The thermally conductive filler is composed of boron nitride and silane coupling agent in a mass ratio of 1:0.5-0.

8. S1-2. Using ethylene-vinyl acetate as the matrix, add 30-40% flame retardant by mass of the ethylene-vinyl acetate, dry at 95-105°C for 3.5-4.5 hours, and then extrude at 200-220°C to obtain a flame retardant intermediate layer. S1-3. Using thermoplastic polyurethane as the base material, add 5-8% modified nano-TiO2 and 2-3% silicone masterbatch by mass of the thermoplastic polyurethane, and extrude at a temperature of 200-220℃ to obtain a UV-resistant outer layer; after surface treatment, combine it with a flame-retardant intermediate layer and a thermally conductive inner layer in sequence through a hot press roller under a pressure of 0.5-1.0MPa and a temperature of 25-180℃ to obtain a composite functional layer.

4. The heat-resistant cross-linked polyethylene insulated power cable as described in claim 3, characterized in that, The flame retardant is composed of aluminum hydroxide and zinc borate compounded in a mass ratio of 2 to 3:

1.

5. A heat-resistant cross-linked polyethylene insulated power cable as described in claim 3, characterized in that, In S1-3, the preparation method of the modified nano-TiO2 is as follows: The nano-TiO2 was divided into 2 to 3 parts. One part was ultrasonically dispersed in ethanol with a silane coupling agent at a mass ratio of 1:0.3 for 30 min. After drying, the first modified TiO2 was obtained. The remaining 1-2 parts of nano-TiO2, 5-8% mica tape (by weight of the nano-TiO2), and 0.5-2% aminosilane (by weight of the nano-TiO2) are subjected to plasma treatment at a power of 45-50W for 50-60 seconds to obtain the second modified TiO2. The first modified TiO2 and the second modified TiO2 are then mixed at a mass ratio of 1:1 to obtain modified nano-TiO2.

6. The heat-resistant cross-linked polyethylene insulated power cable as described in claim 3, characterized in that, In S1-3, the surface treatment method is as follows: ultraviolet light irradiation treatment is performed on each layer, with an irradiation wavelength of 254~365nm, an irradiation intensity of 50~100mW / cm², and a treatment time of 30~120s.

7. A heat-resistant cross-linked polyethylene insulated power cable as described in claim 3, characterized in that, In S1-3, the UV-resistant outer layer and the flame-retardant intermediate layer, as well as the flame-retardant intermediate layer and the heat-conducting inner layer, are all composited using a segmented composite process during the hot press roller bonding process. First stage: Pressurize at 0.5MPa and 180℃ for 15~30s, then add 1~3wt% of epoxy modified silicone resin to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer, and apply microwave-ultrasonic composite field treatment for 10~20s, wherein the microwave power is 200~500W and the ultrasonic frequency is 20~40kHz; Second stage: Pressurize at 1.0MPa and 120℃ for 15~30s. During the pressurization process, add 1~2wt% of nano-silver antibacterial agent to the contact surface between the UV-resistant outer layer and the flame-retardant intermediate layer / the contact surface between the flame-retardant intermediate layer and the thermally conductive inner layer. Then apply microwave-ultrasound composite field treatment for 15~25s, where the microwave power is 100~300W and the ultrasonic frequency is 15~30kHz. The third stage: pressurize at 0.8 MPa and 25-30℃, holding the pressure for 30-60 seconds.

8. A method for preparing a heat-resistant cross-linked polyethylene insulated power cable according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Take 3-5 copper wires and twist them together to obtain 2-4 sets of conductor cores. Then, mix, stir, defoam, extrude and coat the semi-conductive cross-linked polyethylene, silicone resin, nano montmorillonite and HALS light stabilizer onto the surface of the conductor cores to obtain an insulation layer. S2. Then, the conductor cores with insulation layers in each group are twisted together, and the plasticized fiberglass cloth, polyphenylene sulfide and rare earth oxides are mixed, defoamed, extruded and filled into the gaps of the twisted conductor cores to obtain a filling layer. S3. Apply an adhesive to the outside of the insulation layer and the filling layer and bond it to the composite functional layer. Wrap two layers of aluminum-plated steel strip around the composite functional layer to obtain the steel strip armor layer. Finally, wrap the sheath layer around the steel strip armor layer to obtain the power cable.

9. The method for preparing a heat-resistant cross-linked polyethylene insulated power cable as described in claim 8, characterized in that, The adhesive is a silicone rubber-based adhesive.

10. The method for preparing a heat-resistant cross-linked polyethylene insulated power cable as described in claim 1, characterized in that, The initiator is dicumyl peroxide or bis(2,5-diphenyl) peroxide.

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