A crosslinked polyethylene insulated cable and a process for its preparation

Abstract

The application provides a crosslinked polyethylene insulated cable and a preparation process thereof, and belongs to the technical field of cables, and comprises the following steps: step S1, preparing UiO-66-F4 masterbatch; step S2, preparing hexagonal boron nitride masterbatch and nano-alumina masterbatch; step S3, preparing insulation granules; step S4, performing three-layer co-extrusion on a copper core conductor to form a conductor shielding layer / insulation layer / insulation shielding layer, and then performing CV crosslinking, cooling, degassing, and then coating a metal braided shielding layer and an outer sheath to obtain the crosslinked polyethylene insulated cable. The application can improve the DC breakdown strength and long-term insulation stability of the crosslinked polyethylene insulated cable.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and more specifically to a cross-linked polyethylene insulated cable and its manufacturing process. Background Technology

[0002] Cross-linked polyethylene (XLPE) insulated cables are widely used in medium and high voltage power distribution and transmission due to their excellent dielectric properties, good heat resistance, and stable mechanical properties. However, as cables develop towards higher voltage levels, DC transmission, and high current carrying capacity, traditional XLPE insulation has gradually revealed some problems during long-term service. On the one hand, polyethylene material has a low intrinsic thermal conductivity, making it difficult for heat to dissipate in a timely manner during cable operation. This can easily lead to the formation of local hot spots and accelerate thermo-oxidative aging, potentially causing a decrease in the long-term stability of the insulation material. On the other hand, under DC or pulse voltage stress, charge injection and space charge accumulation may occur inside the insulation, causing electric field distortion and resulting in an increase in local field strength. When defects are present or the electric field stress is high, this further increases the risk of failures such as electrical treeing, partial discharge, and dielectric breakdown.

[0003] Some existing technologies improve thermal conductivity and mechanical properties by introducing inorganic fillers. However, due to the high surface energy and poor compatibility of inorganic fillers with polyethylene, if effective surface modification and dispersion control are lacking, the fillers are prone to agglomeration and defects such as debonding, voids, or microcracks at the interface. These defects may become electrical weaknesses, causing a decrease or increased fluctuation in electrical performance indicators such as insulation resistance and breakdown strength. They may also lead to an increase in melt viscosity and a decrease in melt fluidity, thereby worsening the stability of extrusion processing and affecting the long-term operational reliability of cables.

[0004] Patent application CN108503926A discloses a polyethylene insulated overhead cable material, made from the following raw materials in parts by weight: polyethylene, 70-80; natural rubber, 15-20; carbon black N550, 35-45; plasticizer Mediaplast NB-7, 5-8; plasticizer DEDB, 10-15; antioxidant A, 3-5; vulcanizing agent BP, 1-2; vulcanizing agent DCP, 1-2; diatomaceous earth, 20-40; white smoke activator PEG 4000, 0.6; accelerator TMTD, 1-2; fumed silica, 12-16; modified talc, 10-15. This scheme improves the weather resistance and durability of cable materials by adding carbon black and inorganic fillers; however, under high filling conditions, if there is a lack of effective surface modification / interface coupling and dispersion control, carbon black and high specific surface area inorganic fillers are prone to agglomeration and the formation of interface defects, which may cause problems such as local electric field distortion and volume resistivity reduction, thus which is detrimental to the electrical performance and long-term insulation stability of cable materials.

[0005] Therefore, there is a need to provide a cross-linked polyethylene insulated cable and its manufacturing process to solve the problems existing in the prior art. Summary of the Invention

[0006] In view of this, the present invention provides a cross-linked polyethylene insulated cable and its manufacturing process, which can improve the DC breakdown strength and long-term insulation stability of the cross-linked polyethylene insulated cable.

[0007] To achieve the above objectives, the present invention provides a process for manufacturing cross-linked polyethylene insulated cables, comprising the following steps:

[0008] Step S1: Modify UiO-66-F4 with vinyltriethoxysilane to obtain vinylsilane-modified UiO-66-F4 powder, mix it with LLDPE (linear low-density polyethylene) and then extrude and granulate it to obtain UiO-66-F4 masterbatch.

[0009] Step S2: Mix silane-modified hexagonal boron nitride and LLDPE, and extrude and granulate to obtain hexagonal boron nitride masterbatch; mix silane-modified nano-alumina and LLDPE, and extrude and granulate to obtain nano-alumina masterbatch;

[0010] Step S3: Mix LDPE (low-density polyethylene), LLDPE, hexagonal boron nitride masterbatch, nano alumina masterbatch, UiO-66-F4 masterbatch, antioxidant and TAIC (trimethylene isocyanurate), heat and knead, cool down, add DCP (dicumyl peroxide) and knead, extrude and granulate to obtain insulating granules.

[0011] Step S4: The copper core conductor is co-extruded in three layers to form a conductor shielding layer / insulation layer / insulation shielding layer, then cross-linked by CV (continuous vulcanization), cooled, degassed, and then covered with a metal braided shielding layer and an outer sheath to obtain a cross-linked polyethylene insulated cable.

[0012] In this scheme, UiO-66-F4, hexagonal boron nitride, and nano-alumina are modified by silanization and then subjected to masterbatch treatment. This transforms the filler surface from a high surface energy, easily agglomerated state to a wettable state with an organic compatibility layer, thereby significantly improving the dispersion stability of the filler in polyethylene melt and enhancing the filler-matrix interface bonding, reducing interfacial debonding, micropores, and dielectric constant abrupt changes caused by agglomeration. The reason for this is that silane hydrolysis and condensation can form a relatively stable silane layer / siloxane network on the filler surface, improving compatibility and wetting with the polyethylene phase; the masterbatch process provides more sufficient melt shearing and pre-dispersion, allowing the filler to be distributed more uniformly in the matrix at a smaller characteristic scale, thus reducing macroscopic performance dispersion.

[0013] When the filler is finely dispersed, the effective interfacial area increases, allowing the charge trapping and deep trapping effects of UiO-66-F4 at the polyethylene interface, the interfacial polarization suppression and trap energy level regulation effects of nano-alumina, and the thermal conductivity network construction effect of hexagonal boron nitride to be more fully utilized. This reduces the local electric field distortion caused by carrier migration and space charge accumulation, reduces the internal temperature rise and temperature gradient of the insulation layer, and improves the electrical performance stability of the material under long-term electrothermal stress.

[0014] In the mixing stage of insulating granules, a process window control of "first heating to fully disperse, then cooling to add DCP" is adopted. Combined with TAIC crosslinking aid, this improves the uniformity and network density of the crosslinking reaction while suppressing scorching and the formation of gel-hard particles, reducing microscopic hard spots and crack sources caused by uneven crosslinking. Therefore, this invention achieves a comprehensive improvement in the DC breakdown strength, insulation resistance, thermal conductivity, and mechanical properties of cables through the combined effects of reduced defect density, homogenized crosslinking network, and full utilization of functional fillers, thereby enhancing cable stability.

[0015] Preferably, in step S1, the modification step is as follows: anhydrous toluene and UiO-66-F4 powder are mixed, stirred and ultrasonically dispersed, then vinyltriethoxysilane, deionized water and glacial acetic acid are added, the mixture is heated and stirred to react, filtered, washed, and vacuum dried to obtain vinylsilane-modified UiO-66-F4 powder; the UiO-66-F4 masterbatch comprises the following parts by weight of raw materials: 95-115 parts of LLDPE particles and 5-6 parts of vinylsilane-modified UiO-66-F4 powder.

[0016] Vinyltriethoxysilane is used to introduce reaction sites on the surface of UiO-66-F4 that can chemically connect with the polyethylene crosslinking system, thereby enhancing the filler-matrix interface bonding, reducing interface debonding and micropore formation, and thus improving the cable breakdown strength and insulation stability.

[0017] Preferably, the heating and stirring reaction is carried out at a temperature of 50-70°C, a speed of 600-800 rpm, and a time of 3-5 hours.

[0018] Preferably, in step S2, the preparation of silane-modified hexagonal boron nitride includes the following steps:

[0019] Anhydrous ethanol, deionized water, and hexagonal boron nitride were mixed, sonicated, and the pH was adjusted. Vinyltriethoxysilane and octyltriethoxysilane were added, and the mixture was heated to 55-65℃ and stirred at 600-800 rpm for 1.5-2.5 h to obtain silane-modified hexagonal boron nitride.

[0020] Hexagonal boron nitride is modified by synergistic modification of vinyltriethoxysilane and octyltriethoxysilane. The vinyl groups can graft / co-crosslink with polyethylene segments in the DCP / TAIC free radical crosslinking system, thereby enhancing interfacial bonding and helping to reduce interfacial thermal resistance. The octylalkyl chains can improve the hydrophobicity and wettability of the filler surface, reducing lamellar agglomeration and interfacial voids. Therefore, a more continuous thermally conductive network can be constructed without reducing cable insulation, improving cable thermal conductivity and reducing operating temperature rise, thereby mitigating thermo-oxidative aging and electrothermal coupling failure.

[0021] Preferably, in step S2, the preparation of silane-modified nano-alumina includes the following steps:

[0022] Anhydrous ethanol, deionized water, and nano-alumina were mixed, sonicated, and the pH was adjusted. Vinyltriethoxysilane and octyltriethoxysilane were added, and the mixture was heated to 55-65℃ and stirred at 400-600 rpm for 1.5-2.5 h to obtain silane-modified nano-alumina.

[0023] Nano-alumina has a large specific surface area and strong interfacial interaction, which can form high-density interfacial regions and introduce charge trapping sites in polyethylene systems, thereby inhibiting carrier migration and space charge accumulation to a certain extent and reducing electric field distortion. However, untreated nano-alumina is prone to water absorption and hard agglomeration, and the enhanced interfacial polarity can introduce electrical weaknesses such as holes and microcracks. This invention uses vinyltriethoxysilane and octyltriethoxysilane to modify nano-alumina with silane, forming a hydrophobic silane layer on the particle surface and introducing vinyl reaction sites that can participate in crosslinking. This allows the nano-alumina to be networked and more uniformly dispersed during the crosslinking process, thereby reducing interfacial defects caused by agglomeration and water absorption, and improving insulation resistance, DC breakdown strength and mechanical properties.

[0024] Preferably, in step S2, the extrusion granulation temperature is 120-140℃ and the rotation speed is 200-350rpm.

[0025] Preferably, in step S3, 2-vinylanthraquinone masterbatch is also added for mixing; the preparation of the 2-vinylanthraquinone masterbatch includes the following steps:

[0026] LLDPE granules and 2-vinylanthraquinone were mixed at 900-1100 rpm for 3-5 min, and then extruded and granulated. The barrel temperature was set to 110-130℃, the screw speed was set to 200-350 rpm, and vacuum exhaust was turned on. The vacuum degree was -0.08 to -0.06 MPa to obtain 2-vinylanthraquinone masterbatch.

[0027] 2-Vinylanthraquinone molecules possess an anthraquinone conjugated system and a carbonyl group. Their electron acceptor properties enable them to trap injected electrons under high electric fields, reducing effective carrier mobility and mitigating the localized electric field enhancement caused by space charge accumulation. This contributes to improving the DC breakdown strength and electrical aging stability of cables. Simultaneously, 2-vinylanthraquinone contains vinyl groups, making it more prone to grafting or co-crosslinking under peroxide-induced free radical reaction conditions. This makes it more likely to be fixed within the crosslinked network, reducing long-term performance degradation caused by migration and precipitation. By compounding 2-vinylanthraquinone with LLDPE to form masterbatches, uniform dispersion is achieved, reducing dielectric loss fluctuations or electrical weaknesses caused by localized enrichment, thereby further enhancing the insulation stability of cables.

[0028] Preferably, in step S3, the insulating granules comprise the following components in parts by weight:

[0029] 78-80 parts LDPE, 19-21 parts LLDPE, 1.5-3 parts hexagonal boron nitride masterbatch, 0.5-1.5 parts nano alumina masterbatch, 1-2.5 parts UiO-66-F4 masterbatch, 0.2-0.25 parts antioxidant 1010, 0.08-0.12 parts antioxidant 168, 0.8-1 parts TAIC and 1.9-2.3 parts DCP.

[0030] Preferably, in step S4, the temperature of the heating section in the CV crosslinking process is 180-220℃, the temperature of the crosslinking section is 250-320℃, the pressure is 0.8-1.2MPa, and the residence time is 4-6min.

[0031] To achieve the above objectives, the present invention also provides a cross-linked polyethylene insulated cable prepared by the above-described cross-linked polyethylene insulated cable preparation process.

[0032] The DC breakdown strength and long-term insulation stability of cross-linked polyethylene insulated cables prepared using the process of this invention are improved.

[0033] The above-described technical solution of the present invention has at least the following beneficial effects:

[0034] 1. By modifying UiO-66-F4 with vinylsilane and granulating it, interfacial chemical anchoring and interfacial trap density can be achieved in the crosslinking system, which can effectively reduce filler agglomeration, interfacial voids and space charge accumulation, thereby improving the DC breakdown strength and insulation resistance of insulated cables.

[0035] 2. By modifying hexagonal boron nitride with vinyl / octyl bissilane and granulating it, its dispersibility and interfacial thermal conductivity in polyethylene are improved while ensuring insulation. A continuous thermally conductive network is constructed, which improves the thermal conductivity of the insulation layer, reduces the operating temperature rise, and thus slows down thermal-oxidative aging and improves the current carrying capacity of the cable.

[0036] 3. By modifying nano-alumina with bissilane and granulating it, it helps to form a more stable interfacial functional region and reduce the risk of defects caused by water absorption and hard agglomeration. It also takes into account charge trap regulation and interfacial polarization suppression, thereby helping to improve the insulation resistance, DC breakdown strength and mechanical properties of the cable. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are some embodiments of the present invention, and all other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0038] In the following examples, the conductor shielding material and the insulating shielding material are both common commercially available cross-linked semi-conductive shielding materials, the metal braided shielding layer is tin-plated soft copper wire braided shielding material, and the outer sheath is polyvinyl chloride.

[0039] Example 1

[0040] 400 mL of anhydrous toluene and 10 g of UiO-66-F4 powder were mixed, stirred at 600 rpm, and ultrasonically dispersed for 15 min. Then, 0.4 g of vinyltriethoxysilane, 1.2 mL of deionized water, and 0.25 mL of glacial acetic acid were added. The mixture was heated to 60 °C and stirred at 700 rpm for 4 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain vinylsilane-modified UiO-66-F4 powder. 105 g of LLDPE granules were added to a mixer and mixed at 1000 rpm for 1.5 min. Then, 5.5 g of vinylsilane-modified UiO-66-F4 powder was added, and mixing continued for 4 min. The mixture was then transferred to a twin-screw extruder with the barrel temperature set to 130 °C and the screw speed set to 270 rpm. Vacuum exhaust was turned on, and the vacuum degree was -0.07 MPa. The mixture was extruded and granulated to obtain UiO-66-F4 masterbatch.

[0041] Mix 300 mL of anhydrous ethanol, 10 mL of deionized water, and 10 g of hexagonal boron nitride, and sonicate for 25 min. Adjust the pH to 4 with glacial acetic acid, then add 0.2 g of vinyltriethoxysilane and 0.45 g of octyltriethoxysilane. Heat to 60 °C and stir at 700 rpm for 2 h. Filter, wash twice with anhydrous ethanol, and vacuum dry at 80 °C for 10 h to obtain silane-modified hexagonal boron nitride. Add 80 g of LLDPE granules to a mixer and mix at 1000 rpm for 1.5 min. Add 20 g of silane-modified hexagonal boron nitride and continue mixing for 4 min. Transfer to a twin-screw extruder, set the barrel temperature to 130 °C, the screw speed to 270 rpm, and turn on vacuum exhaust to a vacuum degree of -0.07 MPa. Extrude and granulate to obtain hexagonal boron nitride masterbatch.

[0042] Mix 600 mL of anhydrous ethanol, 15 mL of deionized water, and 15 g of nano-alumina. Sonicate the mixture for 15 min, then adjust the pH to 5 with glacial acetic acid. Add 0.3 g of vinyltriethoxysilane and 0.8 g of octyltriethoxysilane, heat to 60 °C, and stir at 500 rpm for 2 h. Filter, wash twice with anhydrous ethanol, and vacuum dry at 80 °C for 10 h to obtain silane-modified nano-alumina. Add 90 g of LLDPE granules to a mixer and mix at 800 rpm for 2 min. Add 10 g of silane-modified nano-alumina and continue mixing for 5 min. Transfer the mixture to a twin-screw extruder, set the barrel temperature to 130 °C, the screw speed to 250 rpm, and turn on vacuum exhaust to a vacuum degree of -0.07 MPa. Extrude and granulate to obtain nano-alumina masterbatch.

[0043] 90g of LLDPE granules and 10g of 2-vinylanthraquinone were mixed at 1000rpm for 4min, extruded and granulated. The barrel temperature was set to 120℃, the screw speed was set to 350rpm, and vacuum exhaust was turned on with a vacuum degree of -0.06MPa to obtain 2-vinylanthraquinone masterbatch.

[0044] 80g LDPE, 19g LLDPE, 2.5g hexagonal boron nitride masterbatch, 1g nano alumina masterbatch, 2g UiO-66-F4 masterbatch, 4g 2-vinylanthraquinone masterbatch, 0.2g antioxidant 1010, 0.12g antioxidant 168 and 1g TAIC were mixed and dispersed evenly, heated to 105℃, kneaded for 5min, cooled to 95℃, 2.1g DCP was added and kneaded for 75s, the discharge temperature was controlled at 105℃, and extruded and granulated to obtain insulating granules.

[0045] The copper core conductor is preheated to 55°C and subjected to three-layer co-extrusion. Conductor shielding material, insulating granules, and insulating shielding material are added to three extruders respectively. The barrel temperature is set to 115°C and the die head temperature to 123°C. After extrusion, CV crosslinking is performed. The temperature of the heating section is set to 200°C and the temperature of the crosslinking section is set to 280°C. The pressure inside the tube is controlled to 1MPa of nitrogen CV and the residence time is 5 minutes. After cooling and degassing, a metal braided shielding layer and an outer sheath are then wrapped to obtain a crosslinked polyethylene insulated cable.

[0046] Example 2

[0047] 400 mL of anhydrous toluene and 10 g of UiO-66-F4 powder were mixed and stirred at 600 rpm and ultrasonically dispersed for 15 min. Then, 0.2 g of vinyltriethoxysilane, 0.4 mL of deionized water and 0.1 mL of glacial acetic acid were added, and the mixture was heated to 70 °C and stirred at 800 rpm for 3 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain vinylsilane-modified UiO-66-F4 powder. 95 g of LLDPE granules were added to a mixer and mixed at 1200 rpm for 1 min. Then, 5 g of vinylsilane-modified UiO-66-F4 powder was added and the mixture was continued for 3 min. The mixture was then transferred to a twin-screw extruder with the barrel temperature set to 140 °C and the screw speed set to 350 rpm. Vacuum exhaust was turned on, and the vacuum degree was -0.08 MPa. The mixture was then extruded and granulated to obtain UiO-66-F4 masterbatch.

[0048] 750 mL of anhydrous ethanol, 25 mL of deionized water, and 25 g of hexagonal boron nitride were mixed and sonicated for 25 min. The pH was adjusted to 5 with glacial acetic acid, followed by the addition of 0.25 g of vinyltriethoxysilane and 0.75 g of octyltriethoxysilane. The mixture was heated to 65 °C and stirred at 600 rpm for 2.5 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain silane-modified hexagonal boron nitride. 80 g of LLDPE granules were added to a mixer and mixed at 800 rpm for 2 min. Then, 20 g of the silane-modified hexagonal boron nitride was added, and mixing continued for 5 min. The mixture was then transferred to a twin-screw extruder with the barrel temperature set to 120 °C and the screw speed set to 200 rpm. Vacuum was turned on to exhaust the air, and the vacuum degree was -0.08 MPa. The mixture was then extruded and granulated to obtain hexagonal boron nitride masterbatch.

[0049] Mix 600 mL of anhydrous ethanol, 15 mL of deionized water, and 15 g of nano-alumina. Sonicate the mixture for 15 min, then adjust the pH to 4 with glacial acetic acid. Add 0.45 g of vinyltriethoxysilane and 1.2 g of octyltriethoxysilane, heat to 55 °C, and stir at 400 rpm for 2.5 h. Filter, wash twice with anhydrous ethanol, and vacuum dry at 80 °C for 10 h to obtain silane-modified nano-alumina. Add 90 g of LLDPE granules to a mixer and mix at 1200 rpm for 1 min. Add 10 g of silane-modified nano-alumina and continue mixing for 3 min. Transfer the mixture to a twin-screw extruder, set the barrel temperature to 120 °C, the screw speed to 200 rpm, and turn on vacuum exhaust to a vacuum degree of -0.06 MPa. Extrude and granulate to obtain nano-alumina masterbatch.

[0050] 90g of LLDPE granules and 10g of 2-vinylanthraquinone were mixed at 900rpm for 5min, extruded and granulated. The barrel temperature was set to 110℃, the screw speed was set to 200rpm, and vacuum exhaust was turned on with a vacuum degree of -0.08MPa to obtain 2-vinylanthraquinone masterbatch.

[0051] 78g LDPE, 21g LLDPE, 3g hexagonal boron nitride masterbatch, 0.5g nano alumina masterbatch, 1g UiO-66-F4 masterbatch, 5g 2-vinylanthraquinone masterbatch, 0.25g antioxidant 1010, 0.08g antioxidant 168 and 0.8g TAIC were mixed and dispersed evenly, heated to 110℃, kneaded for 3min, cooled to 100℃, 2.3g DCP was added and kneaded for 60s, the discharge temperature was controlled at 100℃, and extruded and granulated to obtain insulating granules.

[0052] The copper core conductor is preheated to 55°C and subjected to three-layer co-extrusion. Conductor shielding material, insulating granules, and insulating shielding material are added to three extruders respectively. The barrel temperature is set to 125°C and the die head temperature is set to 130°C. After extrusion, CV crosslinking is performed. The temperature of the heating section is set to 220°C and the temperature of the crosslinking section is set to 320°C. The pressure inside the tube is controlled to nitrogen CV 0.8MPa and the residence time is 4min. After cooling and degassing, a metal braided shielding layer and an outer sheath are then wrapped to obtain a crosslinked polyethylene insulated cable.

[0053] Example 3

[0054] 400 mL of anhydrous toluene and 10 g of UiO-66-F4 powder were mixed and ultrasonically dispersed at 600 rpm for 15 min. Then, 0.6 g of vinyltriethoxysilane, 2 mL of deionized water, and 0.4 mL of glacial acetic acid were added. The mixture was heated to 50 °C and stirred at 600 rpm for 5 h. After filtration, the mixture was washed twice with anhydrous ethanol and vacuum dried at 80 °C for 10 h to obtain vinylsilane-modified UiO-66-F4 powder. 115 g of LLDPE granules were added to a mixer and mixed at 800 rpm for 2 min. Then, 6 g of vinylsilane-modified UiO-66-F4 powder was added and the mixture was continued for 5 min. The mixture was then transferred to a twin-screw extruder with the barrel temperature set to 120 °C and the screw speed set to 200 rpm. Vacuum exhaust was turned on, and the vacuum degree was -0.06 MPa. The mixture was extruded and granulated to obtain UiO-66-F4 masterbatch.

[0055] 750 mL of anhydrous ethanol, 25 mL of deionized water, and 25 g of hexagonal boron nitride were mixed and sonicated for 25 min. The pH was adjusted to 4 with glacial acetic acid, followed by the addition of 0.75 g of vinyltriethoxysilane and 1.5 g of octyltriethoxysilane. The mixture was heated to 55 °C and stirred at 800 rpm for 1.5 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain silane-modified hexagonal boron nitride. 80 g of LLDPE granules were added to a mixer and mixed at 1200 rpm for 1 min. Then, 20 g of the silane-modified hexagonal boron nitride was added, and mixing continued for 3 min. The mixture was then transferred to a twin-screw extruder with a barrel temperature of 140 °C and a screw speed of 350 rpm. Vacuum was applied to achieve a vacuum of -0.06 MPa. The mixture was then extruded and granulated to obtain hexagonal boron nitride masterbatch.

[0056] Mix 600 mL of anhydrous ethanol, 15 mL of deionized water, and 15 g of nano-alumina. Sonicate the mixture for 15 min, then adjust the pH to 5 with glacial acetic acid. Add 0.15 g of vinyltriethoxysilane and 0.3 g of octyltriethoxysilane, heat to 65 °C, and stir at 600 rpm for 1.5 h. Filter, wash twice with anhydrous ethanol, and vacuum dry at 80 °C for 10 h to obtain silane-modified nano-alumina. Add 90 g of LLDPE granules to a mixer and mix at 800 rpm for 2 min. Add 10 g of silane-modified nano-alumina and continue mixing for 5 min. Transfer the mixture to a twin-screw extruder, set the barrel temperature to 140 °C, the screw speed to 350 rpm, and turn on vacuum exhaust to a vacuum degree of -0.08 MPa. Extrude and granulate to obtain nano-alumina masterbatch.

[0057] 90g of LLDPE granules and 10g of 2-vinylanthraquinone were mixed at 1100rpm for 3min, extruded and granulated. The barrel temperature was set to 130℃, the screw speed was set to 350rpm, and vacuum exhaust was turned on with a vacuum degree of -0.06MPa to obtain 2-vinylanthraquinone masterbatch.

[0058] 80g LDPE, 19g LLDPE, 1.5g hexagonal boron nitride masterbatch, 1.5g nano alumina masterbatch, 2.5g UiO-66-F4 masterbatch, 2.5g 2-vinylanthraquinone masterbatch, 0.2g antioxidant 1010, 0.12g antioxidant 168 and 1g TAIC are mixed and dispersed evenly, heated to 100℃, kneaded for 6min, cooled to 90℃, 1.9g DCP is added and kneaded for 90s, the discharge temperature is controlled at 105℃, and extruded and granulated to obtain insulating granules.

[0059] The copper core conductor is preheated to 55°C and subjected to three-layer co-extrusion. Conductor shielding material, insulating granules, and insulating shielding material are added to three extruders respectively. The barrel temperature is set to 105°C and the die head temperature to 115°C. After extrusion, CV crosslinking is performed. The temperature of the heating section is set to 180°C and the temperature of the crosslinking section is set to 250°C. The pressure inside the tube is controlled to nitrogen CV 1.2MPa and the residence time is 6min. After cooling and degassing, a metal braided shielding layer and an outer sheath are then wrapped to obtain a crosslinked polyethylene insulated cable.

[0060] Example 4

[0061] 400 mL of anhydrous toluene and 10 g of UiO-66-F4 powder were mixed, stirred at 600 rpm, and ultrasonically dispersed for 15 min. Then, 0.4 g of vinyltriethoxysilane, 1.2 mL of deionized water, and 0.25 mL of glacial acetic acid were added. The mixture was heated to 60 °C and stirred at 700 rpm for 4 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain vinylsilane-modified UiO-66-F4 powder. 105 g of LLDPE granules were added to a mixer and mixed at 1000 rpm for 1.5 min. Then, 5.5 g of vinylsilane-modified UiO-66-F4 powder was added, and mixing continued for 4 min. The mixture was then transferred to a twin-screw extruder with the barrel temperature set to 130 °C and the screw speed set to 270 rpm. Vacuum exhaust was turned on, and the vacuum degree was -0.07 MPa. The mixture was extruded and granulated to obtain UiO-66-F4 masterbatch.

[0062] 750 mL of anhydrous ethanol, 25 mL of deionized water, and 25 g of hexagonal boron nitride were mixed and sonicated for 25 min. The pH was adjusted to 5 with glacial acetic acid, followed by the addition of 0.25 g of vinyltriethoxysilane and 0.75 g of octyltriethoxysilane. The mixture was heated to 65 °C and stirred at 600 rpm for 2.5 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain silane-modified hexagonal boron nitride. 80 g of LLDPE granules were added to a mixer and mixed at 800 rpm for 2 min. Then, 20 g of the silane-modified hexagonal boron nitride was added, and mixing continued for 5 min. The mixture was then transferred to a twin-screw extruder with the barrel temperature set to 120 °C and the screw speed set to 200 rpm. Vacuum was turned on to exhaust the air, and the vacuum degree was -0.08 MPa. The mixture was then extruded and granulated to obtain hexagonal boron nitride masterbatch.

[0063] Mix 600 mL of anhydrous ethanol, 15 mL of deionized water, and 15 g of nano-alumina. Sonicate the mixture for 15 min, then adjust the pH to 5 with glacial acetic acid. Add 0.15 g of vinyltriethoxysilane and 0.3 g of octyltriethoxysilane, heat to 65 °C, and stir at 600 rpm for 1.5 h. Filter, wash twice with anhydrous ethanol, and vacuum dry at 80 °C for 10 h to obtain silane-modified nano-alumina. Add 90 g of LLDPE granules to a mixer and mix at 800 rpm for 2 min. Add 10 g of silane-modified nano-alumina and continue mixing for 5 min. Transfer the mixture to a twin-screw extruder, set the barrel temperature to 140 °C, the screw speed to 350 rpm, and turn on vacuum exhaust to a vacuum degree of -0.08 MPa. Extrude and granulate to obtain nano-alumina masterbatch.

[0064] 90g of LLDPE granules and 10g of 2-vinylanthraquinone were mixed at 900rpm for 5min, extruded and granulated. The barrel temperature was set to 110℃, the screw speed was set to 200rpm, and vacuum exhaust was turned on with a vacuum degree of -0.08MPa to obtain 2-vinylanthraquinone masterbatch.

[0065] 80g LDPE, 19g LLDPE, 1.5g hexagonal boron nitride masterbatch, 1.5g nano alumina masterbatch, 2.5g UiO-66-F4 masterbatch, 2.5g 2-vinylanthraquinone masterbatch, 0.2g antioxidant 1010, 0.12g antioxidant 168 and 1g TAIC are mixed and dispersed evenly, heated to 100℃, kneaded for 6min, cooled to 90℃, 1.9g DCP is added and kneaded for 90s, the discharge temperature is controlled at 105℃, and extruded and granulated to obtain insulating granules.

[0066] The copper core conductor is preheated to 55°C and subjected to three-layer co-extrusion. Conductor shielding material, insulating granules, and insulating shielding material are added to three extruders respectively. The barrel temperature is set to 115°C and the die head temperature to 123°C. After extrusion, CV crosslinking is performed. The temperature of the heating section is set to 200°C and the temperature of the crosslinking section is set to 280°C. The pressure inside the tube is controlled to 1MPa of nitrogen CV and the residence time is 5 minutes. After cooling and degassing, a metal braided shielding layer and an outer sheath are then wrapped to obtain a crosslinked polyethylene insulated cable.

[0067] Example 5

[0068] 400 mL of anhydrous toluene and 10 g of UiO-66-F4 powder were mixed and stirred at 600 rpm and ultrasonically dispersed for 15 min. Then, 0.2 g of vinyltriethoxysilane, 0.4 mL of deionized water and 0.1 mL of glacial acetic acid were added, and the mixture was heated to 70 °C and stirred at 800 rpm for 3 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain vinylsilane-modified UiO-66-F4 powder. 95 g of LLDPE granules were added to a mixer and mixed at 1200 rpm for 1 min. Then, 5 g of vinylsilane-modified UiO-66-F4 powder was added and the mixture was continued for 3 min. The mixture was then transferred to a twin-screw extruder with the barrel temperature set to 140 °C and the screw speed set to 350 rpm. Vacuum exhaust was turned on, and the vacuum degree was -0.08 MPa. The mixture was then extruded and granulated to obtain UiO-66-F4 masterbatch.

[0069] 750 mL of anhydrous ethanol, 25 mL of deionized water, and 25 g of hexagonal boron nitride were mixed and sonicated for 25 min. The pH was adjusted to 4 with glacial acetic acid, followed by the addition of 0.75 g of vinyltriethoxysilane and 1.5 g of octyltriethoxysilane. The mixture was heated to 55 °C and stirred at 800 rpm for 1.5 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain silane-modified hexagonal boron nitride. 80 g of LLDPE granules were added to a mixer and mixed at 1200 rpm for 1 min. Then, 20 g of the silane-modified hexagonal boron nitride was added, and mixing continued for 3 min. The mixture was then transferred to a twin-screw extruder with a barrel temperature of 140 °C and a screw speed of 350 rpm. Vacuum was applied to achieve a vacuum of -0.06 MPa. The mixture was then extruded and granulated to obtain hexagonal boron nitride masterbatch.

[0070] Mix 600 mL of anhydrous ethanol, 15 mL of deionized water, and 15 g of nano-alumina. Sonicate the mixture for 15 min, then adjust the pH to 4.5 with glacial acetic acid. Add 0.3 g of vinyltriethoxysilane and 0.75 g of octyltriethoxysilane, heat to 60 °C, and stir at 500 rpm for 2 h. Filter, wash twice with anhydrous ethanol, and vacuum dry at 80 °C for 10 h to obtain silane-modified nano-alumina. Add 90 g of LLDPE granules to a mixer and mix at 1100 rpm for 1.5 min. Add 10 g of silane-modified nano-alumina and continue mixing for 4 min. Transfer the mixture to a twin-screw extruder, set the barrel temperature to 125 °C, the screw speed to 300 rpm, and turn on vacuum exhaust to a vacuum degree of -0.07 MPa. Extrude and granulate to obtain nano-alumina masterbatch.

[0071] 90g of LLDPE granules and 10g of 2-vinylanthraquinone were mixed at 950rpm for 4min, extruded and granulated. The barrel temperature was set to 115℃, the screw speed was set to 250rpm, and vacuum exhaust was turned on with a vacuum degree of -0.07MPa to obtain 2-vinylanthraquinone masterbatch.

[0072] 79g LDPE, 20g LLDPE, 2.5g hexagonal boron nitride masterbatch, 1g nano alumina masterbatch, 1.8g UiO-66-F4 masterbatch, 3.7g 2-vinylanthraquinone masterbatch, 0.23g antioxidant 1010, 0.1g antioxidant 168 and 0.9g TAIC were mixed and dispersed evenly, heated to 105℃, and kneaded for 4.5min. The mixture was then cooled to 95℃, and 2.1g DCP was added and kneaded for 75s. The discharge temperature was controlled at 100℃, and the mixture was extruded and granulated to obtain insulating granules.

[0073] The copper core conductor is preheated to 55°C and subjected to three-layer co-extrusion. Conductor shielding material, insulating granules, and insulating shielding material are added to three extruders respectively. The barrel temperature is set to 120°C and the die head temperature to 125°C. After extrusion, CV crosslinking is performed. The temperature of the heating section is set to 195°C and the temperature of the crosslinking section is set to 285°C. The pressure inside the tube is controlled to nitrogen CV 0.95MPa and the residence time is 5min. After cooling and degassing, a metal braided shielding layer and an outer sheath are then wrapped to obtain a crosslinked polyethylene insulated cable.

[0074] Example 6

[0075] 400 mL of anhydrous toluene and 10 g of UiO-66-F4 powder were mixed and stirred at 600 rpm and ultrasonically dispersed for 15 min. Then, 0.2 g of vinyltriethoxysilane, 0.4 mL of deionized water and 0.1 mL of glacial acetic acid were added, and the mixture was heated to 70 °C and stirred at 800 rpm for 3 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain vinylsilane-modified UiO-66-F4 powder. 95 g of LLDPE granules were added to a mixer and mixed at 1200 rpm for 1 min. Then, 5 g of vinylsilane-modified UiO-66-F4 powder was added and the mixture was continued for 3 min. The mixture was then transferred to a twin-screw extruder with the barrel temperature set to 140 °C and the screw speed set to 350 rpm. Vacuum exhaust was turned on, and the vacuum degree was -0.08 MPa. The mixture was then extruded and granulated to obtain UiO-66-F4 masterbatch.

[0076] 750 mL of anhydrous ethanol, 25 mL of deionized water, and 25 g of hexagonal boron nitride were mixed and sonicated for 25 min. The pH was adjusted to 4 with glacial acetic acid, followed by the addition of 0.75 g of vinyltriethoxysilane and 1.5 g of octyltriethoxysilane. The mixture was heated to 55 °C and stirred at 800 rpm for 1.5 h. After filtration, the mixture was washed twice with anhydrous ethanol and dried under vacuum at 80 °C for 10 h to obtain silane-modified hexagonal boron nitride. 80 g of LLDPE granules were added to a mixer and mixed at 1200 rpm for 1 min. Then, 20 g of the silane-modified hexagonal boron nitride was added, and mixing continued for 3 min. The mixture was then transferred to a twin-screw extruder with a barrel temperature of 140 °C and a screw speed of 350 rpm. Vacuum was applied to achieve a vacuum of -0.06 MPa. The mixture was then extruded and granulated to obtain hexagonal boron nitride masterbatch.

[0077] Mix 600 mL of anhydrous ethanol, 15 mL of deionized water, and 15 g of nano-alumina. Sonicate the mixture for 15 min, then adjust the pH to 4.5 with glacial acetic acid. Add 0.3 g of vinyltriethoxysilane and 0.75 g of octyltriethoxysilane, heat to 60 °C, and stir at 500 rpm for 2 h. Filter, wash twice with anhydrous ethanol, and vacuum dry at 80 °C for 10 h to obtain silane-modified nano-alumina. Add 90 g of LLDPE granules to a mixer and mix at 1100 rpm for 1.5 min. Add 10 g of silane-modified nano-alumina and continue mixing for 4 min. Transfer the mixture to a twin-screw extruder, set the barrel temperature to 125 °C, the screw speed to 300 rpm, and turn on vacuum exhaust to a vacuum degree of -0.07 MPa. Extrude and granulate to obtain nano-alumina masterbatch.

[0078] 79g LDPE, 20g LLDPE, 2.5g hexagonal boron nitride masterbatch, 1g nano alumina masterbatch, 1.8g UiO-66-F4 masterbatch, 0.23g antioxidant 1010, 0.1g antioxidant 168 and 0.9g TAIC were mixed and dispersed evenly, heated to 105℃, kneaded for 4.5min, cooled to 95℃, 2.1g DCP was added and kneaded for 75s, the discharge temperature was controlled at 100℃, and extruded and granulated to obtain insulating granules.

[0079] The copper core conductor is preheated to 55°C and subjected to three-layer co-extrusion. Conductor shielding material, insulating granules, and insulating shielding material are added to three extruders respectively. The barrel temperature is set to 120°C and the die head temperature to 125°C. After extrusion, CV crosslinking is performed. The temperature of the heating section is set to 195°C and the temperature of the crosslinking section is set to 285°C. The pressure inside the tube is controlled to nitrogen CV 0.95MPa and the residence time is 5min. After cooling and degassing, a metal braided shielding layer and an outer sheath are then wrapped to obtain a crosslinked polyethylene insulated cable.

[0080] The present invention also includes comparative examples and related experiments.

[0081] Comparative Example 1

[0082] The only difference between Comparative Example 1 and Example 1 is that the vinylsilane-modified UiO-66-F4 was not prepared, but instead UiO-66-F4 was used. The other components and preparation process were the same as in Example 1, and a cross-linked polyethylene insulated cable was prepared.

[0083] Comparative Example 2

[0084] The difference between Comparative Example 2 and Example 1 is that silane-modified hexagonal boron nitride is not prepared, but hexagonal boron nitride is used instead. The other components and preparation process are the same as in Example 1, and cross-linked polyethylene insulated cables are prepared.

[0085] Comparative Example 3

[0086] The difference between Comparative Example 3 and Example 1 is that silane-modified nano-alumina is not prepared, but nano-alumina is used instead. The other components and preparation process are the same as in Example 1, and cross-linked polyethylene insulated cables are prepared.

[0087] Performance testing

[0088] The cross-linked polyethylene insulated cables prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to performance testing. Insulation resistance was tested according to GB / T 3048.5-2007 "Electrical Performance Test Methods for Wires and Cables - Part 5: Insulation Resistance Test"; DC breakdown strength was tested according to GB / T 1408-2016 "Electrical Strength Test Methods for Insulation Materials"; thermal conductivity was tested according to GB / T 10295-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Heat Flow Meter Method"; and tensile strength and elongation at break were tested according to GB / T 2951-2008 "Mechanical and Physical Properties Test Methods for Cables". The comprehensive test results are shown in Table 1.

[0089] Table 1

[0090]

[0091] As can be seen from Table 1 above, the cross-linked polyethylene insulated cables of Examples 1-6 prepared using the process of this invention are superior to those of Comparative Examples 1-3 in terms of DC breakdown strength, insulation resistance, thermal conductivity, and mechanical properties. This indicates that by modifying UiO-66-F4, hexagonal boron nitride, and nano-alumina with silanization, this invention can effectively reduce micro-defects caused by filler agglomeration and interfacial debonding, enhance the bonding between the filler and the matrix, and construct a more continuous thermally conductive and pressure-resistant structure, thereby significantly improving the electrical strength, insulation stability, and mechanical properties of the cable. Compared with Example 1, Comparative Example 1, which did not modify UiO-66-F4 with vinylsilane, showed the most significant decrease in DC breakdown strength and insulation resistance. This indicates that vinylsilane-modified UiO-66-F4 can form a more stable interface anchor and reduce electrical weaknesses in the crosslinking system, thereby improving the DC breakdown strength and insulation stability of the cable. Comparative Example 2, which did not modify hexagonal boron nitride with silane, showed the most significant decrease in thermal conductivity. This indicates that silane modification of hexagonal boron nitride is beneficial to improving its dispersibility and interfacial thermal conductivity, enhancing the continuity of the thermal conductive network, and thus promoting the improvement of cable insulation stability. Comparative Example 3, which did not modify nano-alumina with silane, showed varying degrees of reduction in DC breakdown strength, insulation resistance, and mechanical properties. This indicates that silane modification of nano-alumina can reduce nano-agglomeration and interfacial defects and improve insulation stability.

[0092] Compared with Example 6, Example 5 showed that after adding 2-vinylanthraquinone masterbatch, the DC breakdown strength and insulation resistance of the cable were improved, while the thermal conductivity and mechanical properties remained basically unchanged, indicating that 2-vinylanthraquinone masterbatch can enhance the electrical performance of the cable.

[0093] The above are preferred embodiments of the present invention. Those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A manufacturing process for cross-linked polyethylene insulated cables, characterized in that, Includes the following steps: Step S1: Modify UiO-66-F4 with vinyltriethoxysilane to obtain vinylsilane-modified UiO-66-F4 powder, mix it with LLDPE and then extrude and granulate it to obtain UiO-66-F4 masterbatch; The modification steps are as follows: Anhydrous toluene and UiO-66-F4 powder are mixed, stirred and ultrasonically dispersed, then vinyltriethoxysilane, deionized water and glacial acetic acid are added, the mixture is heated and stirred to react, filtered, washed, and vacuum dried to obtain vinylsilane-modified UiO-66-F4 powder; the UiO-66-F4 masterbatch comprises the following raw materials in parts by weight: 95-115 parts of LLDPE particles and 5-6 parts of vinylsilane-modified UiO-66-F4 powder; Step S2: Mix silane-modified hexagonal boron nitride and LLDPE, and extrude and granulate to obtain hexagonal boron nitride masterbatch; mix silane-modified nano-alumina and LLDPE, and extrude and granulate to obtain nano-alumina masterbatch; The preparation method of silane-modified hexagonal boron nitride is as follows: anhydrous ethanol, deionized water and hexagonal boron nitride are mixed, ultrasonically treated, pH adjusted, vinyltriethoxysilane and octyltriethoxysilane are added, heated to 55-65℃, and stirred at 600-800 rpm for 1.5-2.5 h to obtain silane-modified hexagonal boron nitride. The preparation method of silane-modified nano-alumina is as follows: anhydrous ethanol, deionized water and nano-alumina are mixed, ultrasonically treated, pH adjusted, vinyltriethoxysilane and octyltriethoxysilane are added, heated to 55-65℃, and stirred at 400-600 rpm for 1.5-2.5 h to obtain silane-modified nano-alumina. Step S3: Mix LDPE, LLDPE, hexagonal boron nitride masterbatch, nano alumina masterbatch, UiO-66-F4 masterbatch, antioxidant and TAIC, heat and knead, cool down, add DCP and knead, extrude and granulate to obtain insulating granules. Step S4: Perform three-layer co-extrusion on the copper core conductor to form a conductor shielding layer / insulation layer / insulation shielding layer, then perform CV cross-linking, cooling, degassing, and then cover with a metal braided shielding layer and an outer sheath to obtain a cross-linked polyethylene insulated cable.

2. The manufacturing process of a cross-linked polyethylene insulated cable according to claim 1, characterized in that, The heating and stirring reaction is carried out at a temperature of 50-70℃, a speed of 600-800 rpm, and a time of 3-5 hours.

3. The manufacturing process of a cross-linked polyethylene insulated cable according to claim 1, characterized in that, In step S2, the extrusion granulation temperature is 120-140℃ and the rotation speed is 200-350rpm.

4. The manufacturing process of a cross-linked polyethylene insulated cable according to claim 1, characterized in that, In step S3, 2-vinylanthraquinone masterbatch is also added for mixing; the preparation of the 2-vinylanthraquinone masterbatch includes the following steps: LLDPE granules and 2-vinylanthraquinone were mixed at 900-1100 rpm for 3-5 min, and then extruded and granulated. The barrel temperature was set to 110-130℃, the screw speed was set to 200-350 rpm, and vacuum exhaust was turned on. The vacuum degree was -0.08 to -0.06 MPa to obtain 2-vinylanthraquinone masterbatch.

5. The manufacturing process of a cross-linked polyethylene insulated cable according to claim 1, characterized in that, In step S3, the insulating granules comprise the following components in parts by weight: 78-80 parts LDPE, 19-21 parts LLDPE, 1.5-3 parts hexagonal boron nitride masterbatch, 0.5-1.5 parts nano alumina masterbatch, 1-2.5 parts UiO-66-F4 masterbatch, 0.2-0.25 parts antioxidant 1010, 0.08-0.12 parts antioxidant 168, 0.8-1 parts TAIC and 1.9-2.3 parts DCP.

6. The manufacturing process of a cross-linked polyethylene insulated cable according to claim 1, characterized in that, In step S4, the temperature of the heating section in the CV crosslinking process is 180-220℃, the temperature of the crosslinking section is 250-320℃, the pressure is 0.8-1.2MPa, and the residence time is 4-6min.

7. A cross-linked polyethylene insulated cable, characterized in that, It is prepared using the manufacturing process of a cross-linked polyethylene insulated cable as described in any one of claims 1-6.

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