Crosslinked polyethylene insulated cotton covered wire with low-temperature frost crack prevention function

Abstract

The invention relates to the technical field of wire and cable manufacturing, and discloses a crosslinked polyethylene insulated cotton covered wire with a low-temperature frost crack prevention function. An insulating layer of the crosslinked polyethylene insulated cotton covered wire comprises linear low-density polyethylene, an ethylene-1-octene copolymer elastomer, porous linear low-density polyethylene carrier resin, a fluorine-containing polymer processing aid and a homogeneous active mixed solution. The homogeneous active mixed solution is composed of vinyl silane, 1-octadecene, high vinyl liquid polybutadiene, an initiator and the like, and is adsorbed in porous carrier resin to prepare a dry silane master batch. All the components are subjected to melt grafting in a double-screw extruder and are formed through coating curing and crosslinking treatment. According to the invention, 1-octadecene and polybutadiene are introduced to construct a flexible cross-linking node, and the physical confinement of the carrier resin and the high-pressure closed foam inhibition process of the extruder are combined, so that the insulating layer has the brittle fracture resistance at-40 DEG C, and meanwhile, the high-temperature dimensional stability and low dielectric loss characteristics are maintained.

Description

Technical Field

[0001] This invention relates to the field of wire and cable manufacturing technology, specifically to a cross-linked polyethylene insulated cloth wire with anti-low-temperature freezing cracking function. Background Technology

[0002] Cross-linked polyethylene (XLPE) insulated wires are widely used in building electrical installations and power grid transmission and distribution projects due to their excellent electrical insulation properties and high current carrying capacity. Conventional XLPE materials possess stable physical and mechanical properties at both normal and high temperatures. However, in extremely cold environments, the mobility of its polymer molecular chains decreases drastically, leading to a relative increase in local crystallinity and a hardened state. When cables are bent, pulled, or subjected to external mechanical impacts in such low-temperature climates, the insulation layer is highly susceptible to embrittlement and cracking, potentially causing electrical accidents such as leakage or short circuits.

[0003] To improve the low-temperature resistance of cross-linked polyethylene, current techniques typically involve adding small-molecule plasticizers to the matrix resin or blending large amounts of polyolefin elastomers with low glass transition temperatures. While this approach can alleviate the low-temperature brittleness of the insulation layer to some extent, it also compromises the overall thermomechanical properties of the material. The addition of large amounts of elastomers dilutes the cross-linkable sites in the matrix resin, leading to a decrease in the overall cross-linking degree of the insulation layer. This results in poorer creep resistance of the cable under overload heating conditions, causing the thermal elongation to exceed standard requirements. Simultaneously, small-molecule plasticizers tend to migrate and seep outwards during long-term temperature-fluctuating operation of the wire, causing the cold-resistant effect to decrease over time.

[0004] Furthermore, in traditional silane crosslinking processes, liquid crosslinking agents and modified monomers are typically applied directly to the surface of resin particles via mechanical stirring. During subsequent extrusion feeding and melting, these free liquid components are prone to premature evaporation upon heating. This not only leads to inaccurate proportions of components actually participating in the grafting reaction but also leaves numerous micropores within the insulation layer due to the vaporization of polar small molecules. These micropores disrupt the density of the insulation layer and provide microscopic migration channels for free moisture and polar impurities, ultimately resulting in an increase in the dielectric loss tangent of the wire, severely impacting the stability and lifespan of high-voltage transmission.

[0005] Therefore, this invention proposes a cross-linked polyethylene insulated wire with anti-low-temperature freezing and cracking function to overcome the shortcomings of the prior art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a cross-linked polyethylene insulated wire with anti-low-temperature freezing and cracking function, which solves the problems of easy hardening and brittle fracture of the insulation layer in existing cross-linked polyethylene insulated wires in extremely cold environments, and the decrease in cross-linking degree and increase in dielectric loss caused by conventional plasticizing modification.

[0007] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a cross-linked polyethylene insulated wire with anti-low-temperature freezing and cracking function, adopting the following technical solution: A cross-linked polyethylene insulated wire with low-temperature freeze-cracking protection, wherein the insulation layer is made of raw materials comprising the following parts by weight: 55.0–82.0 parts by weight of linear low-density polyethylene; 10.0 to 30.0 parts by weight of ethylene-1-octene copolymer elastomer; 8.0–15.0 parts by weight of porous linear low-density polyethylene carrier resin; Fluorine-containing polymer processing aids, 0.02–0.10 parts by weight; 3.29–9.31 parts by weight of homogeneous active mixture; The porous linear low-density polyethylene carrier resin is pre-mixed and adsorbed with the homogeneous active mixture to prepare a dry silane masterbatch, which is then used in extrusion molding. The homogeneous active mixture comprises: Vinyltris(2-methoxyethoxy)silane 1.0 to 3.0 parts by weight; 0.2 to 1.0 parts by weight of 1-octadecene; 2.0 to 5.0 parts by weight of high-vinyl liquid polybutadiene; First-stage initiator: 0.05–0.15 parts by weight; Second-stage initiator: 0.02–0.08 parts by weight; 0.02 to 0.08 parts by weight of silane crosslinking catalyst.

[0008] By adopting the above technical solution, this invention redesigns the microstructure of cross-linked polyethylene. Conventional cross-linked networks are typically characterized by relatively rigid connections, while this solution introduces specific modified monomers to construct flexible cross-linking nodes within the base resin. Specifically, the micropores of the porous linear low-density polyethylene carrier resin act as physical confinement, pre-storing the active solution containing silane, 1-octadecene, and high-vinyl liquid polybutadiene within the pores. This pretreatment effectively prevents premature evaporation of liquid components during extruder feeding, thereby ensuring the accuracy of the formulation ratio.

[0009] As the material enters the extruder, the barrel temperature gradually increases, and the two initiators with different half-lives begin to decompose sequentially according to the temperature gradient, releasing free radicals. These free radicals abstract hydrogen atoms from the main chain of the polyethylene and ethylene-1-octene copolymer elastomer, generating macromolecular free radicals (initiation process: ).

[0010] Under conditions of free radicals, vinyltris(2-methoxyethoxy)silane, 1-octadecene, and high-vinyl liquid polybutadiene undergo concurrent grafting. It is worth noting that the high-vinyl liquid polybutadiene, due to its dense 1,2-vinyl structure, can simultaneously attach multiple polymer backbones; meanwhile, the incorporation of 1-octadecene introduces long aliphatic side chains into the system, forcibly widening the originally tightly packed polymer molecular chain spacing. The silane grafting reaction can be represented as follows: During the extrusion compounding process, fluorinated polymer processing aids migrate outward to the inner wall of the equipment due to melt shearing to reduce interfacial friction. This process suppresses the foaming micropores caused by uneven local heating, keeping the melt in a dense state.

[0011] When the extruded cable comes into contact with moisture, the silane groups grafted onto the main chain hydrolyze to generate silanols. Adjacent silanols then undergo dehydration and condensation under the action of a catalyst, completely forming a Si-O-Si three-dimensional cross-linked network. It is precisely because polybutadiene and 1-octadecene jointly alter the local crystallinity of the polyethylene chain segments that the material retains mobility in its molecular chains even at temperatures as low as -40°C. This allows it to absorb externally applied stress through its own deformation, preventing the insulation layer from becoming brittle. The resulting silane cross-linked network is responsible for maintaining the material's high-temperature dimensional stability. Furthermore, the dense, non-porous structure cuts off the microscopic channels for moisture penetration, ensuring the material's low dielectric loss characteristics.

[0012] Preferably, the gel content of the insulating layer is not less than 79%, and it is subjected to conditions of 200℃ and 20 N / cm. 2 The thermal elongation under load conditions shall not exceed 70%; and the elongation at break of the insulation layer at -40℃ shall not be less than 165%, and the dielectric loss tangent at 90℃ shall not exceed 5.0 × 10⁻⁶. -4 .

[0013] By adopting the above technical solution, the two macroscopic parameters of thermal elongation and gel content directly reflect the perfection of the cross-linked network inside the insulation layer, meeting the requirements for creep resistance and dimensional retention of the cable under overload heating conditions. Meanwhile, the elongation at break at -40℃ is not less than 165%, proving that the insulation layer will not become brittle and crack when bent, laid, or installed in extremely cold climates. The low dielectric loss tangent indicates that no microporous defects have been generated inside the insulation layer, and the amount of unreacted polar small molecules remaining is extremely low, ensuring operational safety during high-voltage transmission.

[0014] Preferably, the first-stage initiator is tert-butyl peroxide; the second-stage initiator is 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane; the silane crosslinking catalyst is dibutyltin dilaurate; the fluorinated polymer processing aid is a copolymer of vinylidene fluoride and hexafluoropropylene; the porous linear low-density polyethylene carrier resin has a porosity of 40% to 60%; the ethylene-1-octene copolymer elastomer has an octene mass content of 25% and a crystallinity of 15%; the high-vinyl liquid polybutadiene has a number average molecular weight of 2000 and a 1,2-vinyl structure mass content of 70%.

[0015] By adopting the above technical solution, the design of the two-stage initiation system effectively expands the processing temperature window. Tert-butyl peroxide has a relatively low decomposition temperature, initiating the grafting reaction in the initial melting stage of extrusion; while 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, with a higher decomposition temperature, continues to play a role in the subsequent high-temperature grafting reaction zone, deepening the monomer conversion rate. This combination avoids the premature local crosslinking or scorching problems easily caused by a single initiator. As for the fluorinated additive, the copolymer of vinylidene fluoride and hexafluoropropylene, due to its significant difference in surface energy compared to polyolefins, its migration film formation rate is relatively fast. The carrier resin maintains a porosity of 40%–60%, providing not only sufficient liquid containment space but also retaining sufficient solid-phase framework support to prevent particle breakage and leakage during screw extrusion. Furthermore, polybutadiene with a number-average molecular weight of 2000 and a 1,2-vinyl content of 70% has a kinematic viscosity that matches the silane solution, facilitating penetration and mixing, and its side-chain double bonds provide dense reaction sites. An elastomer with 25% octene content and 15% crystallinity forms the amorphous low-temperature toughness base that forms the foundation for the entire blend system.

[0016] Preferably, the preparation method of porous linear low-density polyethylene carrier resin includes the following steps: adding linear low-density polyethylene and liquid paraffin at a mass ratio of 1:0.67 to 1:1.5 into a closed reaction vessel, and stirring at 180°C to 200°C to form a homogeneous solution; then cooling to 25°C at a cooling rate of 5°C / min to 10°C / min to cause thermal phase separation and solidification of the homogeneous solution; cryogenically pulverizing the solidified material into particles, and then ultrasonically extracting it in n-hexane solvent to remove the liquid paraffin inside the particles; finally drying under vacuum conditions to obtain porous linear low-density polyethylene carrier resin.

[0017] By employing the above technical solution, utilizing the physical properties of high-temperature eutectic compatibility and low-temperature phase separation between linear low-density polyethylene and liquid paraffin, and controlling the phase coarsening time by setting a cooling rate of 5℃ / min to 10℃ / min, a bicontinuous microstructure is formed between the polymer-enriched phase and the solvent-enriched phase. After removing the internal liquid paraffin using hexane via ultrasonic extraction, what remains in situ are three-dimensionally interconnected homogeneous pores. The carrier resin prepared by this thermally induced phase separation has a high pore connectivity rate, ensuring uniformity during subsequent adsorption of active mixtures and avoiding the liquid distribution fluctuations caused by ordinary mechanical blending within the extruder.

[0018] Preferably, the insulating layer is made from the following raw materials in parts by weight: 70.0 parts by weight of linear low-density polyethylene; 20.0 parts by weight of ethylene-1-octene copolymer elastomer; 10.0 parts by weight of porous linear low-density polyethylene carrier resin; 0.05 parts by weight of fluorinated polymer processing aid; and 6.30 parts by weight of homogeneous active mixture. The porous linear low-density polyethylene carrier resin is pre-mixed and adsorbed with the homogeneous active mixture to form a dry silane masterbatch, which is then used in extrusion molding. The homogeneous active mixture includes: 2.0 parts by weight of vinyltris(2-methoxyethoxy)silane, 0.6 parts by weight of 1-octadecene, 3.5 parts by weight of high-vinyl liquid polybutadiene, 0.10 parts by weight of tert-butyl peroxide, 0.05 parts by weight of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and 0.05 parts by weight of dibutyltin dilaurate.

[0019] By adopting the above technical solution, this formulation establishes a balance between the material's mechanical strength and crosslinking reaction efficiency. 70.0 parts of base resin combined with 20.0 parts of elastomer constructs a continuous phase framework that balances tensile strength and elasticity; the combination of 10.0 parts of carrier resin and 6.30 parts of active liquid ensures that the micropore adsorption is just at the critical saturation state, maximizing the grafting agent concentration while avoiding slippage caused by liquid seepage. The ratio of initiator to catalyst also adapts to the molar concentration requirements of the mixed monomers, maintaining a high conversion rate for side-chain modification and silane crosslinking, thereby stabilizing the final product's overall cold resistance and insulation properties.

[0020] Secondly, the present invention provides a method for preparing cross-linked polyethylene insulated wire with anti-low-temperature freezing and cracking function, using the following technical solution: A method for preparing a cross-linked polyethylene insulated wire with low-temperature freeze-cracking resistance includes the following steps: S1. Mix the specified weight parts of vinyltris(2-methoxyethoxy)silane, 1-octadecene, high vinyl liquid polybutadiene, first-stage initiator, second-stage initiator and silane crosslinking catalyst, and stir to form a homogeneous active mixture. S2. The porous linear low-density polyethylene carrier resin is put into a high-speed mixer, and a homogeneous active mixture is sprayed and continuously stirred so that the homogeneous active mixture is adsorbed into the micropores of the porous linear low-density polyethylene carrier resin to obtain dry silane masterbatch. S3. Linear low-density polyethylene, ethylene-1-octene copolymer elastomer, fluorinated polymer processing aids and dry silane masterbatch are added together to a co-rotating twin-screw extruder with multiple temperature control zones for melting, grafting reaction and three-dimensional network anchoring. S4. The melt homogenized by the co-rotating twin-screw extruder enters the extrusion crosshead and is evenly coated on the outer layer of the metal conductor. After cooling and solidification, it is sent to a warm water or steam environment to complete the cross-linking, resulting in cross-linked polyethylene insulated wire with anti-low-temperature freezing cracking function.

[0021] By adopting the above technical solution, the components in the preparation process are not simply mixed physically, but undergo a series of compatibility and reaction evolutions. In the stage of preparing the active mixture, the long-chain 1-octadecene and liquid polybutadiene actually act as co-solvents, which improve the solubility of polar silane monomers in non-polar polyolefin systems, making the stirred mixture homogeneous. This helps the grafting reaction sites to be evenly distributed in subsequent stages.

[0022] The mixture is then sprayed onto the porous carrier resin, where capillary force confines the active liquid within the micropores. This process delays the direct contact time between the active component and the main resin, effectively preventing premature polymerization or volatilization of the active material due to localized heating in the extruder feeding section.

[0023] When the material is fed into the co-rotating twin-screw extruder, the reaction proceeds sequentially as the different temperature zones advance. Part of the initiator decomposes to generate free radicals, which subsequently abstract hydrogen atoms from the main chain to form a large active molecular chain (PE·). At this point, the large active molecular chain undergoes addition reactions with the carbon-carbon double bonds of silane, 1-octadecene, and liquid polybutadiene. High-vinyl liquid polybutadiene, utilizing its multi-point reaction characteristics, acts as a three-dimensional network anchor during grafting, pre-connecting the relatively loose polyethylene molecular chains into a localized network precursor. To suppress bubbles that may be generated during the grafting reaction and the trace hydrolysis of some silanes, a high-pressure sealed environment for the melt is artificially created by installing flow-blocking elements inside the screw, forcibly suppressing bubble nucleation. Combined with a low-friction fluid layer formed at the die orifice by fluorinated processing aids, this ensures that the melt coating the metal conductor is dense and non-porous.

[0024] Preferably, in step S1, the mixing temperature is controlled at 30℃~50℃ and the stirring time is 10min~15min; in step S2, the temperature inside the high-speed mixer is maintained at 50℃~60℃, the stirring speed is set at 200rpm~300rpm, and the stirring time is 20min~40min.

[0025] By adopting the above technical solution, the relatively low mixing temperature of 30℃ to 50℃ can prevent the initiator from decomposing during the preparation stage, maintaining the activity and stability of the mixture. Maintaining a relatively high temperature of 50℃ to 60℃ inside the high-speed mixer aims to reduce the viscosity of air in the micropores of the carrier resin. The centrifugal force generated by stirring forces the gas out of the pores, allowing the active mixture to completely fill the pores. Under these conditions, the resulting dry silane masterbatch has a high loading capacity and a dry surface, preventing it from adhering to the equipment during feeding.

[0026] Preferably, in step S3, the interior of the co-rotating twin-screw extruder is divided into a melting zone, a grafting reaction zone, and a network anchoring zone from the feed to the discharge direction. The process parameters for each temperature zone of the co-rotating twin-screw extruder are as follows: the barrel temperature of the melting zone is set to 120℃~140℃; the barrel temperature of the grafting reaction zone is set to 165℃~175℃; and the barrel temperature of the network anchoring zone is set to 195℃~210℃. To construct a high-pressure, porosity-suppressing melt sealing environment, a first flow-blocking ring element is installed on the screw configuration at the end of the melting zone; a second flow-blocking ring element is installed at the end of the grafting reaction zone; and the residence time of the material in the closed grafting reaction space constructed by the first and second flow-blocking ring elements is strictly controlled to be 15s~25s.

[0027] By adopting the above technical solution, the temperature gradient setting within the extruder corresponds to the decomposition characteristics of the two-stage initiator. The temperature in the melting zone is controlled near the resin melting point, mainly for melting the material and protecting the active components from premature reaction. The grafting reaction zone relies on two flow-blocking ring elements to form a high-pressure filling zone, using forced shearing and reverse pressure to force the active liquid to diffuse into the polyethylene melt. The residence time is strictly controlled between 15s and 25s to ensure that the silane monomers and modified monomers have sufficient time to occupy the grafting sites. The final network anchoring zone uses a higher temperature to allow the remaining active sites to complete the coupling reaction, thereby fixing the internal microstructure of the material.

[0028] Preferably, in step S4, the extrusion crosshead temperature is set to 200℃~210℃; cooling and curing are carried out in a water bath at 25℃ after uniformly coating the outer layer of the metal conductor; the process parameters for completing the crosslinking process are to process in a constant temperature water bath at 80℃~95℃ or a steam crosslinking chamber at 100℃ for 4h~8h.

[0029] By employing the above technical solution, the high-temperature state of the crosshead is connected with the front-end network anchoring zone, maintaining a low viscosity in the melt to achieve smooth coating extrusion. The extruded cable is directly cooled in a 25°C water bath, and the material rapidly passes through the crystallization zone, allowing the amorphous flexible structure introduced by 1-octadecene and polybutadiene to be solidified and preserved. Subsequent long-term treatment in a warm water or steam environment provides sufficient moisture diffusion dynamics for the siloxane groups grafted onto the molecular chain, enabling them to undergo sufficient hydrolysis and condensation, ultimately forming a cross-linked structure with low-temperature resistance.

[0030] This invention provides a cross-linked polyethylene insulated wire with anti-freezing and cracking function. It has the following beneficial effects: 1. This invention utilizes 1-octadecene and high-vinyl liquid polybutadiene as modifying monomers to participate in silane grafting, constructing cross-linking nodes with long aliphatic side chains in a polyethylene matrix. This structure alters the local crystallinity regularity of the molecular chain segments, allowing the insulation layer to maintain its deformability even at -40°C, thus preventing the cable from becoming brittle under stress in extremely cold climates. Simultaneously, because the three-dimensional cross-linked network ultimately formed by the grafted silane provides structural support, the material's thermal elongation properties at high temperatures remain unaffected, effectively solving the technical problem of conventional processes that rely on large amounts of plasticizers for freeze protection, which leads to a decrease in the degree of cross-linking of the insulation layer.

[0031] 2. This invention employs a porous linear low-density polyethylene carrier resin to pre-adsorb a homogeneous active mixture containing silane and an initiator. Utilizing the physical confinement effect of the micropores within the carrier, the liquid active components are temporarily stored within the pores. This directly prevents the liquid monomers from prematurely evaporating or polymerizing due to heating during the extruder feeding stage. This compounding method ensures the accuracy of the component ratios during extrusion processing, allowing the crosslinking agent and modified monomers to be uniformly dispersed in the polymer matrix, avoiding extrusion fluctuations caused by uneven liquid distribution.

[0032] 3. This invention incorporates flow-blocking ring elements at both ends of the grafting reaction zone of a twin-screw extruder to create a high-pressure, sealed processing environment, and further utilizes fluorinated polymer processing aids. The high-pressure state inside the extruder forcibly suppresses the foaming process caused by grafting reaction byproducts, while the fluorinated aids reduce the coefficient of friction at the melt interface and eliminate local melt fractures. The combination of these two factors eliminates microporous defects within the insulation layer. This dense insulation structure cuts off the migration channels for free moisture and polar impurities, significantly reducing the dielectric loss tangent of the wire and ensuring the reliability of insulation during power transmission. Attached Figure Description

[0033] Figure 1 This is a comparison chart of the degree of crosslinking and thermal elongation properties of the present invention, wherein, Figure 1(a) shows the gel content distribution of Examples 1 to 5 and Comparative Example 1. Figure 1 (b) The thermal elongation distribution of Examples 1 to 5 and Comparative Example 1 at 200°C; Figure 2 This is a comparison diagram of the electrical performance of the insulation system of the present invention, wherein, Figure 2 (a) The logarithmic distribution of volume resistivity at 20°C and 90°C for Examples 1 to 5 and Comparative Examples 1 and 2. Figure 2 (b) The distribution of dielectric loss tangent values ​​at 90°C for Examples 1 to 5 and Comparative Examples 1 and 2; Figure 3 This is a comparison diagram of the rheological control and physical performance of the present invention, wherein, Figure 3 (a) shows the actual insulation layer density distribution of Examples 1 to 5 and Comparative Examples 5 and 6. Figure 3 (b) Distribution of the number of charred particles per kilometer of cable surface for each sample; Figure 4 This is a comparison chart of the physical properties of the present invention under extremely cold conditions, wherein, Figure 4 (a) The distribution of elongation at break at -40°C for Examples 1 to 5 and Comparative Examples 3 and 4. Figure 4 (b) The apparent flexural modulus distribution of Examples 1 to 5 and Comparative Examples 3 and 4 at -40°C. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0036] Linear low-density polyethylene, CAS number 9002-88-4, density is 0.920 g / cm³. 3The melt flow rate (under test conditions of 190℃ and 2.16kg) is 2.0 g / 10min. Ethylene-1-octene copolymer elastomer, CAS No. 26221-73-8, octene content is 25% by mass, crystallinity is 15%. High-vinyl liquid polybutadiene, CAS No. 9003-17-2, number average molecular weight is 2000, 1,2-vinyl structure content is 70% by mass. Vinyltris(2-methoxyethoxy)silane, CAS No. 1067-53-4. 1-Octadene, CAS No. 112-88-9. Tert-butyl peroxide, CAS No. 614-45-9. 2,5-Dimethyl-2,5-bis(tert-butylperoxy)hexane, CAS No. 78-63-7. The fluorinated polymer processing aid is a copolymer of vinylidene fluoride and hexafluoropropylene, CAS No. 9011-17-0. Dibutyltin dilaurate, CAS No. 77-58-7. Liquid paraffin, CAS No. 8012-95-1. n-Hexane, CAS No. 110-54-3.

[0037] Preparation Example 1: This preparation example provides a method for preparing a porous linear low-density polyethylene carrier resin, including the following steps: 100 parts by weight of linear low-density polyethylene resin and 100 parts by weight of liquid paraffin were added to a reactor equipped with a closed stirrer. The mixture was heated to 190°C and stirred at this temperature for 2.5 hours to completely dissolve the linear low-density polyethylene in the liquid paraffin, forming a homogeneous solution. Heating was stopped, and the system was cooled to 25°C at a cooling rate of 7°C / min to induce thermal phase separation and solidification. The solidified material was cryogenically pulverized to produce particles with a diameter of approximately 3 mm. The resulting particles were immersed in n-hexane solvent at a liquid-to-solid mass ratio of 10:1 and ultrasonically extracted at 45°C for 5 hours. The extract was discarded, and fresh n-hexane was added, and the extraction process was repeated three times to remove the internal liquid paraffin. The particles after removing the liquid paraffin were placed in a vacuum drying oven and vacuum dried at 55°C and an absolute pressure of 0.01 MPa for 18 hours to obtain a porous linear low-density polyethylene carrier resin with a porosity of 50%.

[0038] Preparation Example 2: This preparation example provides a method for preparing a porous linear low-density polyethylene carrier resin, including the following steps: 100 parts by weight of linear low-density polyethylene resin and 150 parts by weight of liquid paraffin were added to a reactor equipped with a closed stirrer. The mixture was heated to 200°C and stirred at this temperature for 2 hours to completely dissolve the linear low-density polyethylene in the liquid paraffin, forming a homogeneous solution. Heating was stopped, and the system was cooled to 25°C at a cooling rate of 5°C / min to induce thermal phase separation and solidification. The solidified material was cryogenically pulverized to produce particles with a diameter of approximately 2 mm. The resulting particles were immersed in n-hexane solvent at a liquid-to-solid mass ratio of 10:1 and ultrasonically extracted at 50°C for 4 hours. The extract was discarded, and fresh n-hexane was added, and the extraction process was repeated three times to remove the internal liquid paraffin. The particles after removing the liquid paraffin were placed in a vacuum drying oven and vacuum dried at 60°C and an absolute pressure of 0.01 MPa for 12 hours to obtain a porous linear low-density polyethylene carrier resin with a porosity of 60%.

[0039] Preparation Example 3: This preparation example provides a method for preparing a porous linear low-density polyethylene carrier resin, including the following steps: 100 parts by weight of linear low-density polyethylene resin and 67 parts by weight of liquid paraffin were added to a reactor equipped with a closed stirrer. The mixture was heated to 180°C and stirred at this temperature for 3 hours to completely dissolve the linear low-density polyethylene in the liquid paraffin, forming a homogeneous solution. Heating was stopped, and the system was cooled to 25°C at a cooling rate of 10°C / min to induce thermal phase separation and solidification. The solidified material was cryogenically pulverized to produce particles with a diameter of approximately 4 mm. The resulting particles were immersed in n-hexane solvent at a liquid-to-solid mass ratio of 10:1 and ultrasonically extracted at 40°C for 6 hours. The extract was discarded, and fresh n-hexane was added to repeat the extraction process twice to remove the internal liquid paraffin. The particles after removing the liquid paraffin were placed in a vacuum drying oven and vacuum dried at 50°C and an absolute pressure of 0.01 MPa for 24 hours to obtain a porous linear low-density polyethylene carrier resin with a porosity of 40%.

[0040] Example 1: This example provides a method for preparing cross-linked polyethylene insulated wire with low-temperature freeze-cracking resistance, including the following steps: 2.0 parts by weight of vinyltris(2-methoxyethoxy)silane, 0.6 parts by weight of 1-octadecene, 3.5 parts by weight of high-vinyl liquid polybutadiene, 0.10 parts by weight of tert-butyl peroxide, 0.05 parts by weight of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and 0.05 parts by weight of dibutyltin dilaurate were mixed at 40°C and stirred for 12 minutes to form a homogeneous active mixture. 10.0 parts by weight of the porous linear low-density polyethylene carrier resin with a porosity of 50% obtained in Preparation Example 1 were added to a high-speed mixer equipped with a temperature-controlled jacket, maintaining the internal temperature at 60°C and stirring at 250 rpm. The homogeneous active mixture was sprayed onto the porous linear low-density polyethylene carrier resin and stirred continuously for 30 minutes to allow the homogeneous active mixture to be adsorbed into the micropores, obtaining a dry silane masterbatch.

[0041] 70.0 parts by weight of linear low-density polyethylene, 20.0 parts by weight of ethylene-1-octene copolymer elastomer, 0.05 parts by weight of fluorine-containing polymer processing aid, and the above-mentioned dry silane masterbatch are fed into the main feed port of a co-rotating twin-screw extruder with an aspect ratio of 35 through a loss-in-weight feeding system.

[0042] The first to third zones of the extruder are the melting zone, and the barrel temperature is set at 130°C. A flow-blocking ring element is installed on the screw configuration at the end of the third zone of the extruder to establish the first melt seal.

[0043] The fourth and fifth zones of the extruder are the grafting reaction zones, with the barrel temperature set at 170°C. A second flow-blocking ring element is installed at the end of the fifth zone of the extruder, and the residence time of the material in the enclosed space constructed in the fourth and fifth zones is controlled to be 20 seconds.

[0044] Zones 6 to 8 of the extruder are the network anchoring zones, and the barrel temperature is set to 200℃.

[0045] The homogenized melt from the extruder enters the extrusion crosshead and evenly coats the outer layer of the metal conductor. The temperature of the extrusion crosshead is set to 205℃. The coated cable is then cooled, cured, and wound up in a 25℃ water bath. Finally, the wound cable is placed in a 90℃ constant temperature water bath for 6 hours to complete cross-linking, resulting in cross-linked polyethylene insulated cable.

[0046] Example 2: This example provides a method for preparing cross-linked polyethylene insulated wire with low-temperature freeze-cracking resistance, including the following steps: 1.0 parts by weight of vinyltris(2-methoxyethoxy)silane, 0.2 parts by weight of 1-octadecene, 2.0 parts by weight of high-vinyl liquid polybutadiene, 0.05 parts by weight of tert-butyl peroxide, 0.02 parts by weight of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and 0.02 parts by weight of dibutyltin dilaurate were mixed at 30°C and stirred for 10 minutes to form a homogeneous active mixture. 8.0 parts by weight of the porous linear low-density polyethylene carrier resin with a porosity of 40% obtained in Preparation Example 3 were added to a high-speed mixer, maintaining the internal temperature at 50°C and stirring at 200 rpm. The homogeneous active mixture was sprayed onto the porous linear low-density polyethylene carrier resin and stirred continuously for 20 minutes to obtain a dry silane masterbatch.

[0047] 82.0 parts by weight of linear low-density polyethylene, 10.0 parts by weight of ethylene-1-octene copolymer elastomer, 0.02 parts by weight of fluorine-containing polymer processing aid, and the above-mentioned dry silane masterbatch are added to the main feed port of a co-rotating twin-screw extruder with an aspect ratio of 30.

[0048] The first to third zones of the extruder are the melting zone, and the barrel temperature is set at 120°C. A flow-blocking ring element is installed on the screw configuration at the end of the third zone of the extruder to establish the first melt seal.

[0049] The fourth and fifth zones of the extruder are the grafting reaction zones, and the barrel temperature is set at 165°C. A second flow-blocking ring element is installed at the end of the fifth zone of the extruder, and the residence time of the material in the fourth and fifth zones is controlled to be 15 seconds.

[0050] Zones 6 to 8 of the extruder are the network anchoring zones, and the barrel temperature is set to 195°C.

[0051] The melt enters the extrusion crosshead and coats the outer layer of the metal conductor. The extrusion crosshead temperature is set to 200℃. The coated cable is then cooled, cured, and wound up in a 25℃ water bath. The wound cable is then placed in an 80℃ constant temperature water bath for 8 hours to complete cross-linking, resulting in cross-linked polyethylene insulated cable.

[0052] Example 3: This example provides a method for preparing cross-linked polyethylene insulated wire with low-temperature freeze-cracking resistance, including the following steps: 3.0 parts by weight of vinyltris(2-methoxyethoxy)silane, 1.0 parts by weight of 1-octadecene, 5.0 parts by weight of high-vinyl liquid polybutadiene, 0.15 parts by weight of tert-butyl peroxide, 0.08 parts by weight of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and 0.08 parts by weight of dibutyltin dilaurate were mixed at 50°C and stirred for 15 minutes to form a homogeneous active mixture. 15.0 parts by weight of the porous linear low-density polyethylene carrier resin with a porosity of 60% obtained in Preparation Example 2 were added to a high-speed mixer, maintaining the internal temperature at 55°C and stirring at 300 rpm. The homogeneous active mixture was sprayed onto the porous linear low-density polyethylene carrier resin and stirred continuously for 40 minutes to obtain a dry silane masterbatch.

[0053] 55.0 parts by weight of linear low-density polyethylene, 30.0 parts by weight of ethylene-1-octene copolymer elastomer, 0.10 parts by weight of fluorine-containing polymer processing aid, and the above-mentioned dry silane masterbatch are added to the main feed port of a co-rotating twin-screw extruder with an aspect ratio of 40.

[0054] The first to third zones of the extruder are the melting zone, and the barrel temperature is set at 140°C. A flow-blocking ring element is installed on the screw configuration at the end of the third zone of the extruder to establish the first melt seal.

[0055] The fourth and fifth zones of the extruder are the grafting reaction zones, and the barrel temperature is set at 175°C. A second flow-blocking ring element is installed at the end of the fifth zone of the extruder, and the residence time of the material in the fourth and fifth zones is controlled to be 25 seconds.

[0056] Zones 6 to 8 of the extruder are the network anchoring zones, and the barrel temperature is set to 210℃.

[0057] The melt enters the extrusion crosshead and coats the outer layer of the metal conductor. The extrusion crosshead temperature is set to 210℃. The coated cable is then cooled, cured, and wound up in a 25℃ water bath. The wound cable is then placed in a 100℃ steam crosslinking chamber for 4 hours to complete the crosslinking process, resulting in crosslinked polyethylene insulated cable.

[0058] Example 4: This example provides a method for preparing cross-linked polyethylene insulated wire with low-temperature freeze-cracking resistance, including the following steps: 2.0 parts by weight of vinyltris(2-methoxyethoxy)silane, 0.6 parts by weight of 1-octadecene, 3.5 parts by weight of high-vinyl liquid polybutadiene, 0.10 parts by weight of tert-butyl peroxide, 0.05 parts by weight of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and 0.05 parts by weight of dibutyltin dilaurate were mixed at 40°C and stirred for 12 minutes to form a homogeneous active mixture. 10.0 parts by weight of the porous linear low-density polyethylene carrier resin with a porosity of 50% obtained in Preparation Example 1 were added to a high-speed mixer, and the internal temperature was maintained at 60°C with stirring at a speed of 250 rpm. The homogeneous active mixture was sprayed onto the porous carrier resin and stirred continuously for 30 minutes to obtain a dry silane masterbatch.

[0059] 70.0 parts by weight of linear low-density polyethylene, 20.0 parts by weight of ethylene-1-octene copolymer elastomer, 0.05 parts by weight of fluorine-containing polymer processing aid, and the above-mentioned dry silane masterbatch are added to the main feed port of a co-rotating twin-screw extruder with an aspect ratio of 35.

[0060] The first to third zones of the extruder are the melting zone, and the barrel temperature is set at 135°C. A flow-blocking ring element is installed at the end of the third zone of the extruder to establish the first melt seal.

[0061] The fourth and fifth zones of the extruder are the grafting reaction zones, and the barrel temperature is set at 168℃. A second flow-restricting ring element is installed at the end of the fifth zone of the extruder, and the screw speed of the extruder is adjusted to control the residence time of the material in the fourth and fifth zones to 18 seconds.

[0062] Zones 6 to 8 of the extruder are the network anchoring zones, and the barrel temperature is set to 205°C.

[0063] The melt enters the extrusion crosshead and coats the outer layer of the metal conductor. The extrusion crosshead temperature is set to 205℃. The coated cable is then cooled, cured, and wound up in a 25℃ water bath. The wound cable is then placed in a 95℃ constant temperature water bath for 5 hours to complete cross-linking, resulting in cross-linked polyethylene insulated cable.

[0064] Example 5: This example provides a method for preparing cross-linked polyethylene insulated wire with low-temperature freeze-cracking resistance, including the following steps: 2.0 parts by weight of vinyltris(2-methoxyethoxy)silane, 0.6 parts by weight of 1-octadecene, 3.5 parts by weight of high-vinyl liquid polybutadiene, 0.10 parts by weight of tert-butyl peroxide, 0.05 parts by weight of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and 0.05 parts by weight of dibutyltin dilaurate were mixed at 40°C and stirred for 12 minutes to form a homogeneous active mixture. 10.0 parts by weight of the porous linear low-density polyethylene carrier resin with a porosity of 50% obtained in Preparation Example 1 were added to a high-speed mixer, and the internal temperature was maintained at 60°C with stirring at a speed of 250 rpm. The homogeneous active mixture was sprayed and stirred continuously for 30 minutes to obtain a dry silane masterbatch.

[0065] 75.0 parts by weight of linear low-density polyethylene, 15.0 parts by weight of ethylene-1-octene copolymer elastomer, 0.05 parts by weight of fluorine-containing polymer processing aid, and the above-mentioned dry silane masterbatch are added to the main feed port of a co-rotating twin-screw extruder with an aspect ratio of 35.

[0066] Zones 1 to 3 of the extruder are the melting zone, and the barrel temperature is set at 130°C. A flow-restricting ring element is installed at the end of zone 3 of the extruder.

[0067] The fourth and fifth zones of the extruder are the grafting reaction zones, and the barrel temperature is set at 170°C. A second flow-blocking ring element is installed at the end of the fifth zone of the extruder, and the residence time of the material in the fourth and fifth zones is controlled to be 20 seconds.

[0068] Zones 6 to 8 of the extruder are the network anchoring zones, and the barrel temperature is set to 200℃.

[0069] The melt enters the extrusion crosshead and coats the outer layer of the metal conductor. The extrusion crosshead temperature is set to 205℃. The coated cable is then cooled, cured, and wound up in a 25℃ water bath. The wound cable is then placed in a 90℃ constant temperature water bath for 6 hours to complete cross-linking, resulting in cross-linked polyethylene insulated cable.

[0070] Comparative Example 1: Compared with Example 1, the difference is that the porous linear low-density polyethylene carrier resin obtained in Preparation Example 1 is not used in the formulation. Instead, it is replaced by an equal amount of ordinary linear low-density polyethylene resin particles without pores. The homogeneous active mixture is directly adsorbed on the surface of the resin particles. All other aspects are the same.

[0071] Comparative Example 2: Compared with Example 1, the difference is that 2.0 parts by weight of vinyltris(2-methoxyethoxy)silane were replaced with γ-methacryloyloxypropyltrimethoxysilane, and 0.6 parts by weight of 1-octadecene were replaced with octadecyl acrylate, with the rest being the same.

[0072] Comparative Example 3: The difference from Example 1 is that 1-octadecene is not added to the homogeneous active mixture formulation, while the rest are the same.

[0073] Comparative Example 4: The difference from Example 1 is that high-vinyl liquid polybutadiene is not added to the homogeneous active mixture formulation, while the rest are the same.

[0074] Comparative Example 5: Compared with Example 1, the difference is that the flow-blocking ring element is not installed on the screw configuration at the end of the third and fifth zones of the extruder, but is replaced by a reverse thread conveying element, and no fluorinated polymer processing aid is added to the material formulation, while the rest are the same.

[0075] Comparative Example 6: Compared with Example 1, the difference is that tert-butyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxide)hexane are not added to the homogeneous active mixture formulation, but are replaced with 0.15 parts by weight of dicumyl peroxide, and the rest are the same.

[0076] Test Example 1: Test objective: To test the effect of the spatial confinement effect of the two-stage initiator system combined with the porous carrier on the monomer grafting conversion rate and the construction of the three-dimensional cross-linked network of polyethylene.

[0077] The experimental steps are as follows: Cross-linked polyethylene insulated wires prepared in Examples 1 to 5 and Comparative Example 1 were cut, and the outer metal conductors were stripped off, leaving the tubular insulation layer as the test object. Dumbbell-shaped specimens of specified dimensions were cut from the insulation layer, and the initial cross-sectional area and initial gauge length of the parallel middle portion of the specimen were measured and recorded.

[0078] The dumbbell-shaped specimen was suspended in a heat extension test chamber with the temperature controlled at 200℃. A counterweight was suspended at the lower end of the specimen so that the specimen cross-section was subjected to a stress of 20 N / cm². 2 Mechanical stress was applied. After maintaining this state for 15 minutes, the elongation of the gauge length of the specimen was measured and the thermal elongation was calculated. The counterweight stress was relieved, the specimen was removed and allowed to cool naturally at room temperature for 5 minutes, and the gauge length was measured again to calculate the permanent deformation rate.

[0079] Cut a 0.5 g sample of the insulating layer and chop it into millimeter-sized particles. Weigh the initial mass using an analytical balance. Place the sample in a 120-mesh stainless steel mesh bag, seal it, and place it in a round-bottom flask containing xylene solvent. Add an antioxidant at 1% of the total solvent mass to the xylene solvent to prevent thermo-oxidative degradation of the polymer during boiling. Perform reflux boiling extraction at 140°C for 24 hours to extract the uncrosslinked linear polymer. Remove the mesh bag and dry it in a vacuum drying oven at 150°C until a constant mass is reached. Weigh the extract residue and calculate the gel content by the ratio of the extract residue to the initial mass.

[0080] The experimental results are shown in Table 1: Table 1: Crosslinking degree and thermal elongation test results of Examples 1 to 5 and Comparative Example 1

[0081] in conclusion: According to the appendix Figure 1 Data and references Figure 1 The insulation layer samples in Examples 1 to 5 exhibited high crosslinking degree and network density. Conventional silane crosslinking processes typically struggle to overcome the grafting conversion bottleneck within the short residence time of 15 to 25 seconds in a twin-screw extruder. In this embodiment, the gel content was consistently above 79%, and the high-temperature thermal elongation remained below 70%, indicating that the designed forced monomolecular grafting reaction was effectively executed within the extruder. The pore volume of the porous carrier significantly influenced the final network topology. Example 3, using a higher porosity carrier, not only achieved a gel content of 88.4%, but also demonstrated superior dimensional stability under high-temperature loading compared to Example 2, which used a lower porosity carrier. The abundance of micropore volume affected the dispersion state of the active mixture in the polymer melt and the local reactant concentration. Correspondingly, Comparative Example 1, which did not employ a porous carrier, exhibited insufficient kinetic conditions, with its gel content dropping to 42.1% and experiencing macroscopic deformation exceeding 180% during loading and baking. In the absence of micron-sized confined spaces, the reactant concentration is diluted by the massive polyethylene matrix, and free radicals generated by initiator decomposition are largely consumed during diffusion. This technical solution utilizes the locally high-concentration reaction micro-regions formed instantaneously by the collapse of the porous framework to compensate for the insufficient reactivity of pure vinylsilanes and long-chain α-olefins, thereby improving the grafting efficiency of monomers within the extremely short timeframe of the extrusion process.

[0082] Test Example 2: Test objective: To test the influence of monomer system type and the physical confinement effect of porous carrier on the volume resistivity and dielectric loss tangent of the insulating layer, and to evaluate the generation and distribution of polar conductive impurities inside the cross-linked network.

[0083] The experimental steps are as follows: Cross-linked polyethylene insulated wires prepared in Examples 1 to 5, as well as Comparative Examples 1 and 2, were cut off. The insulation layers at both ends were peeled off to expose the internal metal conductors, leaving a tubular insulation layer with an effective length of 5 meters in the middle as a test sample. The samples were immersed in constant temperature water baths set at 20°C and 90°C, respectively, for 2 hours to allow the samples to reach thermal equilibrium.

[0084] A 500V DC voltage was applied between the metal conductor of the sample and the electrodes of the water bath using a high-resistivity meter. After energizing for 1 minute, the insulation resistance value was read according to GB / T 3048.5 "Electrical Performance Test Methods for Wires and Cables - Part 5: Insulation Resistance Test". The volume resistivity of different samples at 20℃ and 90℃ was calculated based on the effective immersion length of the sample, the outer diameter of the insulation layer, and the outer diameter of the conductor.

[0085] Insulated wire samples from the same batch were taken and tested using a high-voltage Schering bridge and a matching water bath electrode system, referring to GB / T 3048.11 "Electrical Performance Test Methods for Wires and Cables - Part 11: Dielectric Loss Tangent Test". Under an applied power frequency AC voltage, the bridge was balanced, and the dielectric loss tangent value of each sample at 90℃ was recorded to evaluate the response of the material's internal polar components to the alternating electric field.

[0086] The experimental results are shown in Table 2: Table 2: Electrical insulation performance test results of Examples 1 to 5 and Comparative Examples 1 to 2

[0087] in conclusion: Based on the data in Table 2 and referring to the appendix Figure 2 The tubular insulation layer samples from Examples 1 to 5 maintained stable electrical performance at both room temperature and 90°C. In routine testing and evaluation of cross-linked polyethylene high-voltage insulation materials, residual polar impurities within the material undergo dipole orientation polarization under a high-temperature alternating electric field, resulting in an increase in the dielectric loss tangent. In this scheme, the dielectric loss tangent at 90°C in all examples is within 5.0 × 10⁻⁶. -4 Within the following range, the volume resistivity remains at 10 at 90℃. 14The concentrations are on the order of Ω·cm. This indicates a low concentration of free conductive ions and polar oligomers within the insulating network. The formulation uses vinylsilane, which lacks homopolymerization ability, and long-chain α-olefins undergoing degenerative chain transfer as comonomers, reducing the probability of small-molecule self-polymerization forming conductive impurities through the chemical reaction pathway. Comparative Example 2 uses highly reactive γ-methacryloyloxypropyltrimethoxysilane in combination with octadecyl acrylate, resulting in a two-order-of-magnitude decrease in volume resistivity and an increase in dielectric loss tangent to 85.3%. This drastic deterioration in electrical properties is related to the loss of the degenerative chain transfer inhibition effect of the long-chain α-olefin. The highly reactive monomers containing methacrylate and acrylate groups undergo free copolymerization in the extruder, generating polymer oligomers with strongly polar ester groups that become dipole polarization centers and charge transfer carriers under alternating electric fields within the polyethylene matrix. Comparative Example 1, which does not use porous carrier resin, also shows a decrease in insulation resistance. When monomers lack the physical confinement effect of porous carriers, the grafting conversion rate is low, resulting in unreacted free monomers remaining in the formulation system. These residual small molecules migrate and aggregate under subsequent high-temperature conditions, reducing the electrical uniformity of the polyethylene matrix. The test data in this set reflect the synergistic effect of monomer selection and the physical confinement of porous carriers in the preparation of the insulation system, maintaining the insulation performance of cable products by improving the grafting rate and suppressing side reactions.

[0088] Test Example 3: Test objective: To test the inhibitory effect of melt pressure spectrum constructed by extruder choke ring element on the foaming behavior of low molecular weight volatiles, and to evaluate the control effect of two-stage initiator system combined with temperature control gradient on crosslinking premature maturation phenomenon.

[0089] The experimental steps are as follows: Cross-linked polyethylene insulated wires prepared in Examples 1 to 5, as well as Comparative Examples 5 and 6, were taken, and the conductors were stripped while the insulation layer remained. Referring to GB / T 1033.1 "Determination of density of non-foamed plastics – Part 1: Impregnation method", the actual density of the insulation layer sample was measured using a precision density balance containing anhydrous ethanol as the impregnation solution. Five different sections of each sample were tested, and the arithmetic mean was calculated.

[0090] Cable samples of 1000 meters in length were collected from each group. Using an optical defect detector and supplemented by manual inspection, the number of scorched particles with a diameter greater than 0.5 mm on the insulation surface was counted. The total number of scorched particles per kilometer of cable surface was recorded to assess the localized premature cross-linking during the extrusion process.

[0091] Referring to GB / T 2951.11 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 11", standard dumbbell-shaped specimens were cut from the insulation layer and tested using an electronic universal testing machine at a tensile speed of 250 mm / min at a normal temperature of 25°C. The maximum tensile stress borne by the specimen at fracture was recorded, and the tensile strength was calculated.

[0092] The experimental results are shown in Table 3: Table 3: Rheological and physical property test results of Examples 1 to 5 and Comparative Examples 5 to 6

[0093] in conclusion: Based on the data in Table 3 and referring to the appendix Figure 3 The insulation layer samples in Examples 1 to 5 exhibited high density and tensile strength, with fewer scorched particles on the surface. During the thermal decomposition of the peroxide initiator to generate primary free radicals, small-molecule byproduct gases, such as tert-butanol and methane, are released. In conventional extrusion processes, these byproduct gases, along with trace amounts of moisture introduced by the resin, expand within the melt, leading to microporous foaming in the cable insulation layer. This embodiment addresses this by assembling smooth-surfaced flow-blocking ring elements at the ends of zones 3 and 5 of the extruder, combined with a dynamic boundary lubrication film formed on the inner wall of the metal barrel by a trace amount of fluorinated processing aids, thus constructing a closed high-pressure reaction chamber inside the extruder. This pressure spectrum control, encompassing both mechanical and rheological dimensions, allows the internal grafting reaction to occur within a dense, high-pressure melt phase, suppressing gas phase precipitation and expansion. The actual density of all examples was maintained at 0.918 g / cm³. 3 The above. In Comparative Example 5, the flow-blocking ring element was removed, making it impossible to establish a high-pressure melt sealing environment. The gaseous byproducts from the initiator decomposition directly expanded and foamed inside the melt, causing its macroscopic density to decrease to 0.814 g / cm³. 3The resulting loose internal structure caused the tensile strength of the material to decrease to 10.3 MPa. In the absence of a flow-blocking ring, the replacement reverse thread element generated shear friction heat during material transport, causing a localized increase in melt temperature. This led to premature decomposition of the dormant second-stage initiator, leaving 58 charred particles per kilometer on the insulation surface. The half-life matching of the initiator system affected the reaction thermal history. A single conventional initiator (such as DCP) could not adapt to the gradient barrel temperature settings. Its excessively long half-life in the 170°C grafting zone resulted in a large amount of unreacted initiator being carried into the 200°C high-temperature anchoring zone; subsequently, concentrated rapid decomposition occurred in the high-temperature zone, triggering premature crosslinking. The mismatch between reaction kinetics and extrusion rheological time led to the formation of highly crosslinked dead gel clumps (Gel clusters) which were extruded with the melt, creating up to 143 surface defects per kilometer on the cable surface, disrupting the continuity of the polymer matrix and causing a decrease in tensile strength. By decoupling the rheodynamic pressure spectrum from the reaction kinetics time axis, the embodiment reduces process interference during extrusion.

[0094] Test Example 4: Test objective: To test the effect of flexible crosslinking hubs constructed from long-chain α-olefins and high-vinyl liquid polybutadiene on the elongation at break and flexural stiffness of insulating materials in an extreme cold environment of -40°C, and to evaluate the effectiveness of the network topology plasticizing mechanism.

[0095] The experimental steps are as follows: Cross-linked polyethylene insulated wires prepared in Examples 1 to 5, as well as Comparative Examples 3 and 4, were cut, and the outer metal conductors were stripped, leaving the tubular insulation layer as the test object. Referring to GB / T 2951.14 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 14: General Test Methods - Low Temperature Tests", dumbbell-shaped tensile specimens of standard size and rectangular strip specimens for bending tests were cut from the insulation layer, and the initial characteristic dimensions of each specimen were measured and recorded.

[0096] The dumbbell-shaped specimen was placed in an electronic universal testing machine equipped with a low-temperature environment chamber. The temperature of the environment chamber was set to stabilize at -40°C, and the specimen was subjected to 16 hours of conditioning under low-temperature conditions to allow the material to reach thermal equilibrium. Subsequently, the specimen was stretched at a rate of 250 mm / min until fracture, and the low-temperature elongation at break was recorded.

[0097] The rectangular strip specimens were also placed in a cryogenic freezer at -40°C for conditioning. A normal load was applied to the specimens using a three-point bending fixture, and the load-deflection curves were recorded. The apparent flexural modulus of each sample under extremely low temperature conditions was calculated to assess the change in the macroscopic stiffness of the material.

[0098] The experimental results are shown in Table 4: Table 4: Test results of physical properties in extreme cold environments of Examples 1 to 5 and Comparative Examples 3 to 4

[0099] in conclusion: Based on the data in Table 4 and referring to the appendix Figure 4 The insulation samples from Examples 1 to 5 retained a high level of deformation elongation capacity under extremely cold conditions of -40°C, with apparent flexural modulus remaining in the low range. In long-term service evaluations of cables in extremely cold regions, it was observed that the molecular chain segments in the amorphous region of cross-linked polyethylene are prone to freezing when subjected to cryogenic environments. This microscopic chain segment stiffness manifests macroscopically as an increase in material rigidity and brittle fracture under stress. In this embodiment, the long aliphatic side chains retained after 1-octadecene grafting play a topological plasticizing role in the polymer's three-dimensional space. The dangling side chains increase the free volume between molecular chains, hindering the close and orderly arrangement of the polyethylene backbone under low-temperature conditions and delaying the glass transition process. High-vinyl liquid polybutadiene, as a macromolecular co-crosslinking agent, participates in network construction, forming a multi-arm flexible node that replaces the relatively rigid short-chain connection structure in conventional silane crosslinking networks. This flexible crosslinking hub can absorb and dissipate deformation energy through conformational adjustment of molecular chain segments when the material is subjected to external tensile or bending stress. Comparative Example 3, without the addition of 1-octadecene as a comonomer, showed an increased flexural modulus of 875 MPa at -40°C and a decreased elongation at break of 42%. Due to the lack of internal plasticizing effect provided by long-chain aliphatic side groups, the material lost the relative slippage ability of molecular chains in low-temperature environments, exhibiting hardening and brittleness characteristics. Comparative Example 4, without high-vinyl liquid polybutadiene, showed a low-temperature elongation at break of 85%. When the crosslinked network lacks flexible nodes as buffers, the high-density rigid crosslinking points will generate local stress concentration under low-temperature external forces, leading to the nucleation and propagation of microcracks. The test data in this group indicate that the compounding of long-chain α-olefins with liquid rubber macromolecules intervenes in the topological evolution of the crosslinked network, improving the mechanical flexibility and fracture resistance of the insulating material under extreme low-temperature conditions.

[0100] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cross-linked polyethylene insulated wire with anti-low-temperature freezing cracking function, characterized in that, The insulation layer of cross-linked polyethylene insulated cloth wires is made from raw materials comprising the following parts by weight: 55.0–82.0 parts by weight of linear low-density polyethylene; 10.0 to 30.0 parts by weight of ethylene-1-octene copolymer elastomer; 8.0–15.0 parts by weight of porous linear low-density polyethylene carrier resin; Fluorine-containing polymer processing aids, 0.02–0.10 parts by weight; 3.29–9.31 parts by weight of homogeneous active mixture; The porous linear low-density polyethylene carrier resin is pre-mixed and adsorbed with the homogeneous active mixture to prepare a dry silane masterbatch, which is then used in extrusion molding. The homogeneous active mixture comprises: Vinyltris(2-methoxyethoxy)silane 1.0 to 3.0 parts by weight; 0.2 to 1.0 parts by weight of 1-octadecene; 2.0 to 5.0 parts by weight of high-vinyl liquid polybutadiene; First-stage initiator: 0.05–0.15 parts by weight; Second-stage initiator: 0.02–0.08 parts by weight; 0.02 to 0.08 parts by weight of silane crosslinking catalyst.

2. The cross-linked polyethylene insulated wire with anti-low-temperature freezing and cracking function according to claim 1, characterized in that, The gel content of the insulating layer is not less than 79%, and it withstands temperatures of 200℃ and 20 N / cm². 2 The thermal elongation under load conditions is not higher than 70%; and the elongation at break of the insulation layer at -40℃ is not less than 165%, and the dielectric loss tangent at 90℃ is not higher than 5.0 × 10⁻⁶. -4 .

3. The cross-linked polyethylene insulated wire with anti-low-temperature freezing and cracking function according to claim 1, characterized in that, The first-stage initiator is tert-butyl peroxide; the second-stage initiator is 2,5-dimethyl-2,5-bis(tert-butylperoxide)hexane; the silane crosslinking catalyst is dibutyltin dilaurate; and the fluorine-containing polymer processing aid is a copolymer of vinylidene fluoride and hexafluoropropylene.

4. The cross-linked polyethylene insulated wire with anti-low-temperature freezing and cracking function according to claim 1, characterized in that, The porous linear low-density polyethylene carrier resin has a porosity of 40% to 60%; the ethylene-1-octene copolymer elastomer has an octene mass content of 25% and a crystallinity of 15%; the high vinyl liquid polybutadiene has a number average molecular weight of 2000 and a 1,2-vinyl structure mass content of 70%.

5. The cross-linked polyethylene insulated wire with anti-low-temperature freezing and cracking function according to claim 1, characterized in that, The preparation method of the porous linear low-density polyethylene carrier resin includes the following steps: Linear low-density polyethylene and liquid paraffin were added to a sealed reactor at a mass ratio of 1:0.67 to 1:1.5 and stirred at 180°C to 200°C to form a homogeneous solution. The solution was then cooled to 25°C at a cooling rate of 5°C to 10°C per minute to induce thermal phase separation and solidification. The solidified material was cryogenically pulverized into particles and then subjected to ultrasonic extraction in n-hexane solvent to remove the liquid paraffin from the particles. Finally, the mixture was dried under vacuum to obtain the porous linear low-density polyethylene carrier resin.

6. The cross-linked polyethylene insulated wire with anti-low-temperature freezing and cracking function according to claim 1, characterized in that, The insulating layer is made from the following raw materials in parts by weight: 70.0 parts by weight of linear low-density polyethylene; 20.0 parts by weight of ethylene-1-octene copolymer elastomer; 10.0 parts by weight of porous linear low-density polyethylene carrier resin; 0.05 parts by weight of fluorinated polymer processing aid; and 6.30 parts by weight of homogeneous active mixture. The porous linear low-density polyethylene carrier resin is pre-mixed and adsorbed with the homogeneous active mixture to prepare a dry silane masterbatch, which is then used in extrusion molding. The homogeneous active mixture comprises: 2.0 parts by weight of vinyltris(2-methoxyethoxy)silane, 0.6 parts by weight of 1-octadecene, 3.5 parts by weight of high-vinyl liquid polybutadiene, 0.10 parts by weight of tert-butyl peroxide, 0.05 parts by weight of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and 0.05 parts by weight of dibutyltin dilaurate.

7. A method for preparing a cross-linked polyethylene insulated wire with anti-low-temperature freezing cracking function according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Mix the specified weight parts of vinyltris(2-methoxyethoxy)silane, 1-octadecene, high vinyl liquid polybutadiene, first-stage initiator, second-stage initiator and silane crosslinking catalyst, and stir to form a homogeneous active mixture. S2. The porous linear low-density polyethylene carrier resin is put into a high-speed mixer, the homogeneous active mixture is sprayed and continuously stirred, so that the homogeneous active mixture is adsorbed into the micropores of the porous linear low-density polyethylene carrier resin to obtain dry silane masterbatch. S3. The linear low-density polyethylene, the ethylene-1-octene copolymer elastomer, the fluorinated polymer processing aid and the dry silane masterbatch are added together to a co-rotating twin-screw extruder with multiple temperature control zones for melting, grafting reaction and three-dimensional network anchoring. S4. The melt homogenized by the co-rotating twin-screw extruder enters the extrusion crosshead and is evenly coated on the outer layer of the metal conductor. After cooling and solidification, it is sent to a warm water or steam environment for treatment to complete cross-linking, thereby obtaining the cross-linked polyethylene insulated wire with anti-low-temperature freezing cracking function.

8. The method for preparing cross-linked polyethylene insulated wire with anti-low-temperature freezing cracking function according to claim 7, characterized in that, In step S1, the mixing temperature is controlled at 30℃~50℃ and the stirring time is 10min~15min; in step S2, the temperature inside the high-speed mixer is maintained at 50℃~60℃, the stirring speed is set at 200rpm~300rpm, and the stirring time is 20min~40min.

9. The method for preparing cross-linked polyethylene insulated wire with anti-low-temperature freezing cracking function according to claim 7, characterized in that, The specific implementation method of step S3 is as follows: The co-rotating twin-screw extruder is internally divided into a melting zone, a grafting reaction zone, and a network anchoring zone from the feed to the discharge direction. The process parameters for each temperature zone of the co-rotating twin-screw extruder are as follows: the barrel temperature of the melting zone is set to 120℃~140℃; the barrel temperature of the grafting reaction zone is set to 165℃~175℃; and the barrel temperature of the network anchoring zone is set to 195℃~210℃. To create a high-pressure, porosity-suppressing melt sealing environment, a first flow-blocking ring element is installed on the screw configuration at the end of the molten zone; a second flow-blocking ring element is installed at the end of the grafting reaction zone; the residence time of the material in the closed grafting reaction space constructed by the first and second flow-blocking ring elements is strictly controlled to be 15s to 25s.

10. The method for preparing cross-linked polyethylene insulated wire with anti-low-temperature freezing cracking function according to claim 7, characterized in that, In step S4, the temperature of the extrusion crosshead is set to 200℃~210℃; the cooling and curing is carried out in a water bath at 25℃ after uniformly coating the outer layer of the metal conductor; the process parameters for completing the crosslinking process are to process in a constant temperature water bath at 80℃~95℃ or a steam crosslinking chamber at 100℃ for 4h~8h.

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