Composite cross-linked polyethylene insulated cable integrating signal and power transmission

Abstract

The invention relates to the technical field of cables, and discloses a composite cross-linked polyethylene insulated cable integrating signal and power transmission, which comprises a composite wire core, an inner semiconductive shielding layer, a composite cross-linked polyethylene insulating layer and an outer semiconductive shielding layer which are sequentially coated from inside to outside, the composite cross-linked polyethylene insulating layer is prepared by extruding and cross-linking the following raw materials in parts by weight: 90-95 parts of low-density polyethylene particles, 5.42-11.6 parts of a solid premix and 0.7-2.0 parts of a liquid co-solvent; wherein the solid state premix contains N, N '-m-phenylenedimaleimide and tetrabutyl titanate, and the liquid state co-soluble substance contains tetramethyl tetravinyl cyclotetrasiloxane and dicumyl peroxide. By constructing a coordination network to anchor byproducts, space charges and micropores of an insulating layer are eliminated, voltage resistance is improved, signal attenuation is reduced, and long-term stability of power and signal integrated transmission of the composite cable is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of cable technology, specifically to a composite cross-linked polyethylene insulated cable that integrates signal and power transmission. Background Technology

[0002] Insulated cables are the infrastructure for energy transmission in power grids. Cross-linked polyethylene (XLPE) is currently the mainstream insulation matrix material due to its relatively stable dielectric and mechanical properties. With the development of smart grids, integrating signal interaction and power transmission into a single cable, forming a composite XLPE structure that integrates signal and power transmission, has become a requirement for the multi-functional development of modern cables.

[0003] Existing insulation layer manufacturing generally uses peroxide crosslinking technology. The process involves mixing polyethylene resin as the main material with a crosslinking agent, then co-extruding it onto the outside of the wire core using an extruder. The mixture is then fed into a vulcanization pipe and heated to induce crosslinking of macromolecular chains, thus constructing a polymer network with pressure and heat resistance to adapt to power grid operating conditions.

[0004] Existing crosslinking systems and manufacturing processes have shortcomings in practical applications. Peroxide crosslinking agents release polar small-molecule byproducts during high-temperature decomposition. These byproducts tend to migrate freely within the insulating matrix, causing space charge accumulation and localized electric field distortion under the operating electric field, accelerating the aging and breakdown of the insulating material. Furthermore, conventional processes feed all components into the extruder at once, making the crosslinking agent prone to early decomposition due to thermal shearing in the front section of the barrel, leading to localized scorching of the material. In addition, uncontrolled low-boiling-point byproducts vaporize in the high-temperature crosslinking section, leaving microporous defects within the thick-walled insulation layer. This not only weakens the overall withstand voltage but also causes physical scattering and dielectric attenuation of high-frequency signals transmitted within the composite cable, making it difficult for the material to simultaneously meet the dual requirements of high-voltage insulation and low-loss signal transmission.

[0005] Therefore, this invention proposes a composite cross-linked polyethylene insulated cable that integrates signal and power transmission to overcome the shortcomings of the prior art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a composite cross-linked polyethylene insulated cable that integrates signal and power transmission, solving the technical problems of space charge accumulation induced by the migration of cross-linked polar byproducts and signal transmission loss caused by micropore defects inside the thick-walled insulation layer.

[0007] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a composite cross-linked polyethylene insulated cable integrating signal and power transmission, employing the following technical solution: A composite cross-linked polyethylene insulated cable integrating signal and power transmission comprises, from the inside out: a composite core, an inner semi-conductive shielding layer, a composite cross-linked polyethylene insulation layer, and an outer semi-conductive shielding layer; the composite cross-linked polyethylene insulation layer is made by extruding and cross-linking raw materials containing the following parts by weight: 90-95 parts of low-density polyethylene particles, 5.42-11.6 parts of solid premix, and 0.7-2.0 parts of liquid co-solution; wherein the solid premix contains N,N'-m-phenylenebismaleimide and tetrabutyl titanate, and the liquid co-solution contains tetramethyltetravinylcyclotetrasiloxane and dicumyl peroxide.

[0008] By adopting the above technical solution, since the present invention processes and combines the coordination component and the siloxane component in solid and liquid forms respectively, it changes the microstructure of the insulation layer after cross-linking and curing. Therefore, it achieves the effect of suppressing space charge accumulation and improving the electrical stability of the cross-linked polyethylene insulation layer.

[0009] The specific process by which this system can suppress charge accumulation mainly manifests in the sequential reactions of multiple components under extrusion and crosslinking conditions. The tetrabutyl titanate contained in the solid premix has titanium atoms with empty orbitals. When the material is in a molten state in the extruder, these titanium atoms coordinate with the carbonyl oxygen atoms of the imide ring on the N,N'-m-phenylenebismaleimide structure in the premix, thereby forming a primary coordination structure with titanium-oxygen coordination bonds as the core inside the insulating matrix.

[0010] Building upon this, as the liquid co-solution is injected into the later stage of extrusion, the tetramethyltetravinylcyclotetrasiloxane, as a cyclic molecule, has oxygen atoms in its siloxane group containing lone pairs of electrons, which can undergo secondary physical complexation with the previously formed titanium coordination centers. This mutual stacking and complexation between different molecules constructs an interstitial structure with certain steric hindrance within the amorphous region of polyethylene.

[0011] When the cable blank to be cross-linked enters the continuous vulcanizing tube for high-temperature cross-linking, dicumyl peroxide undergoes homogenization upon heating, generating free radicals that initiate cross-linking of polyethylene macromolecules. Inevitably, it decomposes and releases polar byproducts such as acetophenone and cumyl alcohol. When these byproducts with polar groups diffuse outward from within the insulation layer and enter the aforementioned interstitial structure, their actual long-distance migration ability is significantly weakened due to the combined limitations of the dipole interaction and electrostatic adsorption of the titanium coordination centers and siloxane rings. Through this dual physical and chemical action, the polar byproducts are in-situ fixed within the intermolecular spaces of the cross-linked polyethylene, fundamentally cutting off the source of space charge formation and accumulation.

[0012] Preferably, the composite cross-linked polyethylene insulation layer is made from raw materials comprising the following parts by weight: 92 parts of low-density polyethylene particles, 8.86 parts of solid premix, and 1.2 parts of liquid co-solution.

[0013] By adopting the above technical solution, the ratio of the insulating matrix resin to each reaction additive can be kept relatively balanced. This not only avoids the problem of increased dielectric loss caused by excessively high total additive concentration, but also prevents the situation where the internal steric hindrance structure is insufficient to completely fix the crosslinking byproducts due to excessively low concentration.

[0014] Preferably, the solid premix comprises the following components in parts by weight: 5-10 parts of low-density polyethylene powder, 0.1-0.5 parts of 4,4'-thiobis(6-tert-butyl-m-cresol), 0.3-1.0 parts of N,N'-m-phenylenebismaleimide, and 0.02-0.10 parts of tetrabutyl titanate.

[0015] By adopting the above technical solution, powdered low-density polyethylene is used as a mixing carrier, which utilizes its large specific surface area to adsorb liquid tetrabutyl titanate and powdered N,N'-m-phenylenebismaleimide, thus solving the problem of uneven macroscopic dispersion of trace additives during the extrusion of the main material. The 4,4'-thiobis(6-tert-butylm-cresol) added in this process is mainly used to ensure the thermo-oxidative stability of the material during the extrusion plasticizing stage.

[0016] Preferably, the liquid co-solution is composed of the following components in parts by weight: 0.2-0.8 parts of tetramethyltetravinylcyclotetrasiloxane and 0.5-1.2 parts of dicumyl peroxide.

[0017] By employing the above technical solution, and utilizing the liquid-phase properties of tetramethyltetravinylcyclotetrasiloxane, dicumyl peroxide, a crosslinking agent that is normally solid at room temperature, is completely dissolved to form a homogeneous liquid. Injecting this liquid material at the rear of the extruder is primarily to avoid localized high-concentration aggregation zones caused by incomplete melting of dicumyl peroxide particles, thereby effectively reducing the risk of early crosslinking and scorching of the insulating material at the extruder head.

[0018] Secondly, the present invention provides a method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission, employing the following technical solution: A method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission includes the following steps: Step 1: Low-density polyethylene granules and solid premix are uniformly mixed using a mixer to obtain the insulating base material to be processed; Step 2: The insulating base material to be processed is added to the main feed port of a twin-screw extruder, and the temperature of the first-stage screw temperature zone is controlled for melting and plasticizing to obtain a plasticized melt containing a coordination network; Step 3: Using a liquid metering pump, the liquid eutectic is injected at constant pressure into the second-stage screw section of the extruder, and the temperature of this section is controlled for mixing to obtain a composite melt containing a pseudo-complex structure; Step 4: The composite melt is introduced into a three-layer co-... Extrusion head, controlling the extrusion head temperature, simultaneously coats the composite core with the inner semiconductive shielding melt and the outer semiconductive shielding melt as the insulating layer material, so that the composite melt is between the inner and outer semiconductive shielding melts, to obtain the cable blank to be cross-linked; Step 5: The cable blank to be cross-linked is fed into a continuous vulcanizing tube for stepped temperature rise cross-linking, to obtain a composite cross-linked polyethylene insulated cable that has completed in-situ grafting and cross-linking; Step 6: The composite cross-linked polyethylene insulated cable is cooled to room temperature in a water-cooling section and then wound up.

[0019] By adopting the above technical solution, the components that are prone to early reactions are isolated in space and time. By introducing them into the extrusion system in stages, the micro-capture network can be orderly constructed inside the insulating material and cross-linking can be completed.

[0020] In the extrusion process of conventional cable insulation materials, if the modifier and crosslinking agent are mixed and added to the extruder at the same time, it often easily triggers localized early crosslinking reactions in the material. To avoid this process risk, this method selects to simultaneously add a solid premix without peroxide crosslinking agent and the polyethylene granule main material through the main feed port. When these mixtures pass through the first-stage screw temperature zone, under the combined action of the strong shear force provided by the screw and specific temperature conditions, the tetrabutyl titanate in the solid component can fully contact N,N'-m-phenylenebismaleimide, thereby completing the initial dynamic coordination bonding in the molten polyethylene matrix. Since the initiator has not been introduced into the material system at this stage, the possibility of scorching of the insulation material in the early stage of plasticization is eliminated from the source.

[0021] After the initial coordination network construction is completed, the plasticized melt is advanced by the screw to the second temperature zone. At this point, a liquid eutectic formed by the miscibility of tetramethyltetravinylcyclotetrasiloxane and dicumyl peroxide is injected at constant pressure through a liquid metering pump. The addition of the liquid component not only improves the processing fluidity of the high-viscosity melt to a certain extent, but more importantly, the siloxane groups it carries can directly form a spatial physical complex with the previously formed titanium-oxygen coordination network. Using this segmented and targeted injection and mixing operation, the main insulating material can evolve into a microscopic pseudo-complex structure containing undecomposed crosslinking agent before being pushed into the three-layer co-extrusion die head. When the extruded cable blank enters the continuous vulcanizing tube and undergoes stepped heating, the polyethylene macromolecular chains begin to crosslink and solidify under the influence of free radicals generated by the homolytic cracking of the initiator. At the same time, the polar small molecule byproducts that are inevitably released during the crosslinking process are intercepted in situ and anchored in the gaps of the newly constructed three-dimensional network, thus cutting off the free charge migration path from the manufacturing source.

[0022] Preferably, in step 1, the solid premix is ​​prepared in advance through the following steps: In a dry environment with a relative humidity of less than 20%, low-density polyethylene powder is mixed with 4,4'-thiobis(6-tert-butyl-m-cresol) at 20-30°C to obtain a basic mixed powder; then N,N'-m-phenylenebismaleimide and tetrabutyl titanate are added to the basic mixed powder, and the mixture is further mixed at 20-30°C to obtain a powdered solid premix.

[0023] By adopting the above technical solution, considering the physicochemical properties of tetrabutyl titanate (TBT) being highly hygroscopic and hydrolyzed, strictly limiting the relative humidity of the mixing environment is a fundamental condition for maintaining its subsequent coordination activity. In the specific formulation process, a physical adsorption method is used to first ensure the antioxidant component adheres uniformly to the large specific surface area of ​​the low-density polyethylene powder; then, the core coordination reaction component is slowly mixed in. This powder blending operation at room temperature avoids premature degradation of the material due to heat, ensuring that the solid premix remains a loose and stable powder phase before entering the extrusion feed port.

[0024] Preferably, in step 3, the liquid co-solution is prepared in advance through the following steps: In a sealed mixing tank that has been purged with dry nitrogen, tetramethyltetravinylcyclotetrasiloxane is added and heated to 42-55°C to obtain a preheated crosslinking modifier; dicumyl peroxide is added to the crosslinking modifier and stirred continuously until completely dissolved to obtain a transparent homogeneous liquid eutectic.

[0025] By adopting the above technical solution, the conventional melting point of dicumyl peroxide is generally around 39°C. Based on this property, preheating tetramethyltetravinylcyclotetrasiloxane, which acts as a solvent environment, to a temperature slightly above this melting point (42-55°C) allows the crosslinking agent, which is originally a solid crystal, to rapidly absorb heat and completely dissolve within it. The batching operation is carried out in a sealed tank purged with dry nitrogen, eliminating interference from ambient oxygen and moisture on the activity of the crosslinking agent. The resulting transparent homogeneous liquid not only improves the accuracy of subsequent high-pressure pump injection but also prevents unmelted particles from entering the extruder with the fluid, which could cause pipeline blockage or localized melt concentration imbalance.

[0026] Preferably, in step 2, the temperature of the first screw section of the twin-screw extruder is controlled at 90-110℃; in step 3, the temperature of the second screw section of the twin-screw extruder is controlled at 110-125℃; and in step 4, the temperature of the three-layer co-extrusion die head is controlled at 125-135℃.

[0027] By adopting the above technical solution, the stepped temperature settings of each section of the extruder and the process rhythm of step-by-step feeding are mutually adapted. Maintaining the first stage at a relatively low temperature range of 90-110℃ basically meets the heat requirements for the transition of low-density polyethylene from solid particles to a continuous molten state, while preventing thermomechanical degradation of the base resin backbone under the initial strong shear force. When the material enters the second stage, the upper temperature limit is appropriately relaxed to 125℃, the direct purpose of which is to reduce the apparent viscosity of the melt; after the viscosity decreases, the newly injected liquid phase can be more easily dispersed and evenly dispersed by the screw engagement elements. As for the extruder head, its processing temperature is defined within a narrow range of 125-135℃, which not only provides the good flowability required for the synchronous co-extrusion bonding of the insulating material and the inner and outer semiconductive shielding layers, but also safely avoids the rapid thermal decomposition critical point of the crosslinking agent, retaining sufficient safety processing margin in the extrusion molding stage.

[0028] Preferably, in step 5, when the cable blank to be cross-linked is fed into the continuous vulcanizing tube, the pressure of the continuous vulcanizing tube is controlled to be 1.0-1.5 MPa.

[0029] By adopting the above technical solution, in the initial stage when the cable blank enters the high-temperature cross-linking tube, the cross-linking agent is prone to precipitating gaseous byproducts due to intense heating. At this time, by applying a continuous pipeline back pressure of 1.0-1.5 MPa by externally filling with nitrogen, these gaseous small molecules can be effectively forced to redissolve in the polymer melt, thereby inhibiting their expansion and formation of micropores inside the insulation layer. This pressure range has undergone structural mechanics balance considerations, which can make the microstructure of the cross-linked insulation layer tend to be dense, while taking into account the structural strength of the newly formed molten blank itself, preventing radial geometric collapse of the soft cable due to external pressure overload.

[0030] Preferably, in step 5, the specific temperature control for the stepped temperature crosslinking is as follows: the temperature of the pre-crosslinking zone is set to 165-175℃, the temperature of the main crosslinking zone is set to 185-195℃, and the temperature of the deep crosslinking zone is set to 205-215℃.

[0031] By adopting the above technical solution and setting a three-stage cross-linking heating program, the radial temperature hysteresis effect caused by heat transfer from the surface to the interior of the thick-walled insulation layer is effectively alleviated. Under the relatively mild thermal radiation in the pre-cross-linking zone, the outermost layer of the cable undergoes a certain degree of light cross-linking first and forms a gelled protective shell, which plays a supporting role in stabilizing the overall roundness of the cable. Subsequently, it enters the main cross-linking zone with a larger temperature range. Relying on the enhanced heat penetration capability, the cross-linking initiator deep in the insulation layer begins to decompose on a large scale, driving the construction of a dense graft network between carbon chain macromolecules. The final deep cross-linking zone mainly undertakes the task of promoting the complete reaction of the residual cross-linking agent, which not only further increases the overall cross-linking degree of the material, but also allows the polar decomposition products in the free state to obtain sufficient molecular thermal kinetic energy to generate sufficient dipole interaction with the nearby already formed coordination gaps, until they are completely locked in the solidified network.

[0032] This invention provides a composite cross-linked polyethylene insulated cable that integrates signal and power transmission. It has the following advantages: 1. This invention constructs a multi-level coordination complex network within the insulating matrix by introducing a solid premix and a liquid eutectic. This network utilizes dipole interactions and physical steric hindrance to anchor the polar byproducts generated by crosslinking within the intermolecular gaps, thus blocking space charge migration. This approach suppresses local electric field distortion and improves the withstand voltage stability of crosslinked polyethylene insulated cables used for power transmission.

[0033] 2. This invention prevents premature decomposition of the initiator by physically isolating components prone to early reactions and employing a stepwise extrusion process that involves pre-plasticizing the solid main material and subsequently injecting the liquid crosslinking agent. The segmented mixing improves melt flowability, eliminates the risk of scorching during insulation extrusion, and ensures a dense coating between the main insulation material and the semi-conductive shielding layer, guaranteeing the interface bonding quality of the composite core.

[0034] 3. This invention alleviates the radial heat transfer temperature difference during heating of thick-walled insulation by applying external back pressure and implementing stepped heating within a continuous vulcanization tube. This process promotes uniform grafting of the macromolecular network, and, combined with high voltage suppression of byproduct vaporization, prevents microporous defects in the matrix. The dense structure reduces dielectric loss, meeting the dielectric requirements for low-attenuation signal interaction within the cable. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the cable structure of the present invention; Figure 2 Figure 1 shows the extrusion processing parameters and early crosslinking tendency test results for each experimental group of the present invention; wherein, Figure (a) shows the main motor current fluctuation rate of each experimental group; and Figure (b) shows the gel content of the extruded preform of each experimental group. Figure 3 Figure 1 shows the distribution of polar byproducts in the insulating layer of each experimental group of the present invention; wherein, Figure (a) shows the distribution of acetophenone content in the insulating layer; and Figure (b) shows the distribution of cumulol content in the insulating layer. Figure 4 Figure 1 shows the crosslinking degree and heat creep performance test results of each experimental group of the present invention; wherein, Figure (a) is the gel content; Figure (b) is the thermal elongation at 200℃; and Figure (c) is the permanent deformation rate at 200℃. Figure 5 Figures show the high-frequency dielectric properties and signal attenuation test results of each experimental group of the present invention; wherein, Figure (a) is the dielectric loss tangent at 1 GHz; Figure (b) is the signal attenuation constant at 1 GHz; and Figure (c) is the attenuation increment after aging. Figure 6 Figure 1 shows the test results of the swelling rate of the semiconductive layer and signal integrity in each experimental group of the present invention; wherein, Figure (a) is the initial light attenuation before aging; Figure (b) is the additional light attenuation after aging; Figure (c) is the volume swelling rate of the inner semiconductive shielding layer; and Figure (d) is the 10Gbps eye diagram jitter increment.

[0036] The components include: 1. Composite core; 2. Inner semiconductive shielding layer; 3. Composite cross-linked polyethylene insulation layer; and 4. Outer semiconductive shielding layer. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] The base resin is high-voltage cable grade low-density polyethylene, CAS number 9002-88-4, with a melt flow rate of 1.5 to 2.5 g / 10 min and a density of 0.910 to 0.925 g / cm³. 3The main initiator is dicumyl peroxide, CAS number 80-43-3. The co-crosslinking agent is N,N'-m-phenylenebismaleimide, CAS number 3006-93-7. The crosslinking modifier is tetramethyltetravinylcyclotetrasiloxane, CAS number 2554-06-5. The complexing bridging agent is tetrabutyl titanate with a purity greater than or equal to 99.0%, CAS number 5593-70-4. The antioxidant is 4,4'-thiobis(6-tert-butyl-m-cresol), CAS number 96-69-5.

[0040] Preparation Example 1: This preparation example provides a method for preparing a solid premix. To avoid moisture interference, the following steps are all carried out in a dry environment with a relative humidity of less than 20%, including the following steps: Step 1: Add 8 parts by weight of low-density polyethylene powder and 0.2 parts by weight of 4,4'-thiobis(6-tert-butyl-m-cresol) to a high-speed kneader and mix at 25°C for 5 minutes to obtain the basic mixed powder. Step 2: Add 0.6 parts by weight of N,N'-m-phenylenebismaleimide and 0.06 parts by weight of tetrabutyl titanate to the basic mixed powder, and continue to mix rapidly at 25°C for 10 minutes to obtain a powdered solid premix in which the additives are fully adsorbed by the carrier and have good flowability.

[0041] Preparation Example 2: This preparation example provides a method for preparing a solid premix. To avoid moisture interference, the following steps are all carried out in a dry environment with a relative humidity of less than 20%, including the following steps: Step 1: Add 5 parts by weight of low-density polyethylene powder and 0.1 parts by weight of 4,4'-thiobis(6-tert-butyl-m-cresol) to a high-speed kneader and mix at 20°C for 5 minutes to obtain the basic mixed powder. Step 2: Add 0.3 parts by weight of N,N'-m-phenylenebismaleimide and 0.02 parts by weight of tetrabutyl titanate to the basic mixed powder, and continue to mix rapidly at 20°C for 10 minutes to obtain a powdered solid premix.

[0042] Preparation Example 3: This preparation example provides a method for preparing a solid premix. To avoid moisture interference, the following steps are all carried out in a dry environment with a relative humidity of less than 20%, including the following steps: Step 1: Add 10 parts by weight of low-density polyethylene powder and 0.5 parts by weight of 4,4'-thiobis(6-tert-butyl-m-cresol) to a high-speed kneader and mix at 30°C for 5 minutes to obtain the basic mixed powder. Step 2: Add 1.0 part by weight of N,N'-m-phenylenebismaleimide and 0.10 parts by weight of tetrabutyl titanate to the basic mixed powder, and continue to mix rapidly at 30°C for 10 minutes to obtain a powdered solid premix.

[0043] Preparation Example 4: This preparation example provides a method for preparing a liquid eutectic, comprising the following steps: Step 1: In a sealed mixing tank that has been purged with dry nitrogen, add 0.4 parts by weight of tetramethyltetravinylcyclotetrasiloxane and heat to 45°C to obtain a preheated crosslinking modifier. Step 2: Add 0.8 parts by weight of dicumyl peroxide to the preheated crosslinking modifier, and stir continuously at 45°C for 20 minutes until completely dissolved to obtain a transparent homogeneous liquid eutectic without any solid particles remaining, so as to ensure the stable operation of the metering pump during subsequent high-pressure injection.

[0044] Preparation Example 5: This preparation example provides a method for preparing a liquid eutectic, comprising the following steps: Step 1: In a sealed mixing tank that has been purged with dry nitrogen, add 0.2 parts by weight of tetramethyltetravinylcyclotetrasiloxane and heat to 42°C to obtain a preheated crosslinking modifier. Step 2: Add 0.5 parts by weight of dicumyl peroxide to the preheated crosslinking modifier, and stir continuously at 42°C for 20 minutes until completely dissolved to obtain a transparent homogeneous liquid eutectic.

[0045] Preparation Example 6: This preparation example provides a method for preparing a liquid eutectic, comprising the following steps: Step 1: In a sealed mixing tank that has been purged with dry nitrogen, add 0.8 parts by weight of tetramethyltetravinylcyclotetrasiloxane and heat to 55°C to obtain a preheated crosslinking modifier. Step 2: Add 1.2 parts by weight of dicumyl peroxide to the preheated crosslinking modifier, and stir continuously at 55°C for 20 minutes until completely dissolved to obtain a transparent homogeneous liquid eutectic.

[0046] Example 1: This example provides a method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission, including the following steps: Step 1: 92 parts by weight of low-density polyethylene granules and 8.86 parts by weight of the solid premix prepared in Preparation Example 1 are uniformly mixed by a mixer to obtain the insulating base material to be processed. Step 2: Add the insulating base material to be processed into the main feed port of the twin-screw extruder, and control the temperature of the first screw temperature zone of the twin-screw extruder to 100°C, so that the base material melts and under strong shear, the tetrabutyl titanate and N,N'-m-phenylenebismaleimide complete dynamic coordination to obtain a plasticized melt containing a coordination network. Step 3: Using a high-pressure liquid metering pump, inject 1.2 parts by weight of the liquid co-solution prepared in Preparation Example 4 into the second screw section of the twin-screw extruder under constant pressure, and control the screw temperature of this section to 118°C, so that the liquid components are uniformly dispersed in the plasticized melt to obtain a composite melt containing a pseudo-complex structure. Step 4: Introduce the composite melt into the three-layer co-extrusion die head, control the temperature of the three-layer co-extrusion die head to 130°C, and use it as the insulation layer material to simultaneously coat the outer layer of the composite core integrating signal and power transmission with the inner semi-conductive shielding material melt and the outer semi-conductive shielding material melt, so that the composite melt is between the inner and outer semi-conductive shielding material melts, and obtain the cross-linked cable blank. Step 5: The cable blank to be cross-linked is fed into a continuous vulcanization tube with a pressure of 1.2MPa for step-by-step temperature cross-linking. The temperatures of the pre-cross-linking zone, the main cross-linking zone and the deep cross-linking zone are set to 170℃, 190℃ and 210℃ respectively, to obtain a composite cross-linked polyethylene insulated cable that has completed in-situ grafting and cross-linking. Step 6: After the composite cross-linked polyethylene insulated cable is cooled to room temperature through a water-cooling section, it is wound up.

[0047] Example 2: This example provides a method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission, including the following steps: Step 1: 95 parts by weight of low-density polyethylene granules and 5.42 parts by weight of the solid premix prepared in Preparation Example 2 are uniformly mixed by a mixer to obtain the insulating base material to be processed. Step 2: Add the insulating base material to be processed into the main feed port of the twin-screw extruder, and control the temperature of the first screw temperature zone to 90℃ for melting and plasticizing to obtain a plasticized melt; Step 3: Using a high-pressure liquid metering pump, inject 0.7 parts by weight of the liquid eutectic obtained from Preparation Example 5 into the second screw section of the extruder under constant pressure, and control the temperature of this section at 110°C for mixing to obtain a composite melt; Step 4: Introduce the composite melt into the three-layer co-extrusion die head, control the die head temperature to 125℃, and use it as the insulation layer material to simultaneously coat the outer layer of the composite core integrating signal and power transmission with the inner semi-conductive shielding material melt and the outer semi-conductive shielding material melt, to obtain the cross-linked cable blank. Step 5: The cable blank to be cross-linked is fed into a continuous vulcanizing tube with a pressure of 1.0 MPa for step-by-step temperature cross-linking. The temperatures of the pre-cross-linking zone, the main cross-linking zone and the deep cross-linking zone are set to 165℃, 185℃ and 205℃ respectively, to obtain a composite cross-linked polyethylene insulated cable that has completed cross-linking. Step 6: After the composite cross-linked polyethylene insulated cable is cooled to room temperature through a water-cooling section, it is wound up.

[0048] Example 3: This example provides a method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission, including the following steps: Step 1: 90 parts by weight of low-density polyethylene granules and 11.6 parts by weight of the solid premix prepared in Preparation Example 3 are uniformly mixed by a mixer to obtain the insulating base material to be processed. Step 2: Add the insulating base material to be processed into the main feed port of the twin-screw extruder, and control the temperature of the first screw temperature zone to 110℃ for melting and plasticizing to obtain a plasticized melt; Step 3: Using a high-pressure liquid metering pump, inject 2.0 parts by weight of the liquid eutectic obtained from Preparation Example 6 into the second screw section of the extruder under constant pressure, and control the temperature of this section at 125°C for mixing to obtain a composite melt; Step 4: Introduce the composite melt into the three-layer co-extrusion die head, control the die head temperature to 135℃, and use it as the insulation layer material to simultaneously coat the outer layer of the composite core integrating signal and power transmission with the inner semi-conductive shielding material melt and the outer semi-conductive shielding material melt, to obtain the cross-linked cable blank. Step 5: The cable blank to be cross-linked is fed into a continuous vulcanizing tube with a pressure of 1.5MPa for step-by-step temperature cross-linking. The temperatures of the pre-cross-linking zone, the main cross-linking zone and the deep cross-linking zone are set to 175℃, 195℃ and 215℃ respectively, to obtain a composite cross-linked polyethylene insulated cable that has completed cross-linking. Step 6: After the composite cross-linked polyethylene insulated cable is cooled to room temperature through a water-cooling section, it is wound up.

[0049] Reference Figure 1 In the above embodiments 1 to 3, the composite cross-linked polyethylene insulated cable integrating signal and power transmission is manufactured, and its structure includes, from the inside to the outside, the following components: composite core 1, inner semiconductive shielding layer 2, composite cross-linked polyethylene insulation layer 3, and outer semiconductive shielding layer 4.

[0050] The melts forming the inner semiconductive shielding layer 2 and the outer semiconductive shielding layer 4 are conventional cross-linked semiconductive material melts made with ethylene-vinyl acetate copolymer as the matrix and filled with conductive carbon black. For example, a cross-linked semiconductive shielding material made by mixing ethylene-vinyl acetate copolymer with a mass fraction of 28% and acetylene conductive carbon black with a mass fraction of 35% can be used. The material forming the composite cross-linked polyethylene insulation layer 3 is the product of the composite melt extruded in the aforementioned preparation step after cross-linking and curing. The composite core 1 integrating signal and power transmission is a conventional optoelectronic composite conductor structure made of multiple stranded copper conductors and optical fibers. For example, a concentric stranded annealed round copper conductor with a cross-sectional area of ​​50 square millimeters can be used as the power transmission carrier, and a stainless steel tube containing a single-mode optical fiber can be stranded in the conductor stranding gap or center position as the signal transmission carrier.

[0051] In one embodiment, the outer semiconductive shielding layer 4 may further include conventional cable protection structures such as a metal shielding layer, a water-blocking tape, an armor layer, and a polyvinyl chloride or polyethylene outer sheath to meet the requirements of different laying environments for the cable's mechanical properties and waterproof and flame-retardant properties.

[0052] Comparative Example 1: The difference from Example 1 is that tetrabutyl titanate was not added in step 2 of preparation example 1, but all other steps were the same.

[0053] Comparative Example 2: Compared with Example 1, the difference is that tetramethyltetravinylcyclotetrasiloxane was not added in step 1 of Preparation Example 4, and only dicumyl peroxide was heated and melted before being injected. The rest were the same.

[0054] Comparative Example 3: Compared with Example 1, the difference is that steps 1, 2 and 3 in Example 1 are combined and replaced with a one-time mixing extrusion process, that is, 92 parts by weight of low-density polyethylene granules, 8.86 parts by weight of the solid premix prepared in Preparation Example 1 and 1.2 parts by weight of the liquid co-solution prepared in Preparation Example 4 are added to the mixer at one time for blending; then all the blended material is added from the main feed port of the twin-screw extruder, and the temperature of the first screw section of the extruder is controlled at 100°C and the temperature of the second screw section is controlled at 118°C to directly obtain the composite melt through melt plasticization. The remaining steps are the same as in Example 1.

[0055] Comparative Example 4: Compared with Example 1, the difference is that N,N'-m-phenylenebismaleimide was not added in step 2 of the preparation of Example 1, and all other steps were the same.

[0056] Test Example 1: Experimental steps: 1. Preparation of experimental subjects: The composite cross-linked polyethylene insulated cable blanks were extruded according to the methods provided in Examples 1 to 3 and Comparative Examples 1 to 4.

[0057] 2. Thirty minutes after feeding into the twin-screw extruder, continuously sample the operating current of the extruder's main motor using a high-frequency power parameter recorder. The sampling time is 20 minutes, and the sampling frequency is 10 times per second. Extract the maximum, minimum, and average current values ​​within the 20-minute period, and calculate the main motor current fluctuation rate using the formula: Main motor current fluctuation rate = (Maximum current - Minimum current) / Average current × 100%.

[0058] 3. After the current test in step 2, a sample of the cable blank to be cross-linked, approximately 20 cm long, is cut from the exit of the three-layer co-extrusion die head. This cut portion is in a state before entering the continuous vulcanization tube. The composite core, inner semiconductive shielding layer, and outer semiconductive shielding layer inside the sample are peeled off, leaving only the middle insulation base material. The insulation base material is then processed into a size less than 1 mm. 3 granules.

[0059] 4. Weigh approximately 0.500 g of the fragmented sample as the initial mass, and place it in a constant-weight 120-mesh stainless steel mesh bag, tying the bag tightly. Place the mesh bag in a round-bottom flask containing xylene solvent and reflux extract at 140°C for 12 hours. After extraction, remove the mesh bag and place it in a vacuum drying oven, drying at 110°C to constant weight. Weigh the total mass of the mesh bag and residue, and subtract the mass of the mesh bag to obtain the mass of insoluble matter. Calculate the gel content of the extruded preform as a percentage of the insoluble matter mass divided by the initial mass, rounding the result to two decimal places.

[0060] Experimental results (see Table 1): Table 1: Extrusion processing parameters and early crosslinking tendency test results for each experimental group

[0061] Test conclusion: According to Table 1 and Figure 2 According to the test data, the main motor current fluctuation rate in Examples 1 to 3 remained below 2.0%, and the gel content of the extruded preform was no higher than 0.05%. This indicates that under this process, the rheological state of the low-density polyethylene melt inside the screw is stable, and dicumyl peroxide does not decompose during the extrusion stage.

[0062] In Comparative Example 3, the liquid component was mixed with solid particles and added to the main feed inlet in a single step, resulting in a significant increase in the main motor current fluctuation rate to 18.63% and a gel content in the extruded preform as high as 4.82%. The physical reason for this is that liquid tetramethyltetravinylcyclotetrasiloxane precipitated in the solid conveying zone at the front of the screw, lubricating the metal surface and causing significant fluctuations in the frictional torque between the material and the screw. Simultaneously, dicumyl peroxide, having undergone prolonged frictional heating and shearing throughout the screw section, prematurely triggered the free radical cross-linking reaction of low-density polyethylene, producing significant scorch products.

[0063] Data from Comparative Examples 1 and 4 show that in the absence of tetrabutyl titanate or N,N'-m-phenylenebismaleimide, the main motor current fluctuation rate increased to 5.26% and 4.71%, respectively. This is because an effective Lewis acid-base coordination network was not constructed within the first-stage screw temperature zone, resulting in a lack of molecular-level constraint on the tetramethyltetravinylcyclotetrasiloxane injected in the second stage. Some of the free liquid migrated towards the melt edge and contacted the inner wall of the barrel due to centrifugal force, causing localized screw slippage.

[0064] The mechanism of Examples 1 to 3 lies in the stable coordination between the carbonyl oxygen of N,N'-m-phenylenebismaleimide and the empty orbital of the titanium atom of tetrabutyl titanate in the first stage, and the spatial complexation between this coordination center and the siloxane oxygen atom of tetramethyltetravinylcyclotetrasiloxane in the second stage. This hierarchical coordination structure stably binds the liquid component within the polyethylene melt, preventing its migration to the metal interface, thereby effectively avoiding the risk of early crosslinking while maintaining processing stability.

[0065] Test Example 2: Experimental steps: 1. Experimental subject preparation: Composite cross-linked polyethylene insulated cables prepared in Examples 1 to 3 and Comparative Examples 1 to 4 and completed by water-cooled winding were selected as experimental subjects. Cable samples with a length of 5 meters were cut and placed in a constant temperature drying oven at 90°C for 168 hours to accelerate the migration process of residual volatile substances inside the insulation layer under thermal stress.

[0066] 2. After thermal accelerated aging, the cable sample was removed and allowed to cool at room temperature for 24 hours. A 2 mm thick cross-sectional slice was cut from the longitudinal middle section of the sample. The composite core integrating signal and power transmission in the center of the slice was manually peeled off, and the inner and outer semiconductive shielding layers were removed, leaving only the cross-linked polyethylene insulation layer.

[0067] 3. Divide the insulating sheet radially into three concentric annular regions of equal thickness. Collect the inner annular material adjacent to the melt of the inner semiconductive shielding material and record it as the inner layer sample; collect the outer annular material adjacent to the melt of the outer semiconductive shielding material and record it as the outer layer sample. Cut each of these two samples into fragments with a mass of approximately 1.0 gram.

[0068] 4. Place each group of debris samples into a 20 mL headspace vial with a PTFE sealing gasket, accurately add 10 mL of anhydrous methanol as the extraction solvent, and seal. Place the headspace vial in an ultrasonic water bath at 40 °C for 4 hours to promote the full mass transfer and dissolution of the polar byproducts inside the insulating material into the methanol solvent.

[0069] 5. After allowing the headspace vial to stand for solid-liquid separation, use a microsyringe to penetrate the PTFE seal and draw 1 μL of clear supernatant. Inject this supernatant into the injection port of a gas chromatograph equipped with a flame ionization detector (FID). The supernatant vaporizes instantaneously at the high-temperature injection port and is carried by nitrogen carrier gas into the capillary column to complete the chromatographic separation of polar molecules. Subsequently, it undergoes combustion ionization in the detector to generate electrical signals for the corresponding substances. This testing procedure is a routine quantitative analysis technique for volatile organic compounds in this field. Record the absorption peak area corresponding to the retention time of the substance in the chromatogram. Based on the concentration-peak area external standard curve of pure acetophenone and pure cyclohexanol pre-plotted in conventional gas chromatography quantitative analysis techniques (i.e., the linear equation obtained by linearly fitting the chromatographic peak areas of standard solutions with known concentration gradients to the chromatogram), substitute the absorption peak area obtained from the sample test into this linear equation to calculate the mass concentration of the corresponding polar substance in the extraction supernatant. Then multiply this mass concentration by the volume of the extractant (10 mL) and divide it by the initial weighing mass of the corresponding group of debris sample to finally convert the absolute mass fraction of acetophenone and cyclohexanol in the inner and outer layer samples. Record the data in ppm (mg / kg).

[0070] Experimental results (see Table 2): Table 2: Test results of polar byproduct content distribution in the inner and outer layers of the insulation layer for each experimental group

[0071] Test conclusion: According to Table 2 and Figure 3 The data shows that in Examples 1 to 3, the content differences of acetophenone and cumyl alcohol in the outer and inner layers are minimal, maintaining a stable radial distribution. Based on the volatilization kinetics of polymer materials under constant temperature and forced-air conditions, it is known that the outer layer of cable insulation is in direct contact with flowing hot air, and its internal low-molecular-weight volatiles typically dissipate rapidly into the external environment; while the inner layer, hindered by the outer layer, allows volatiles to more easily penetrate and remain in the internal voids. After 168 hours of high-temperature baking, the insulation layer in the examples showed no significant loss of polar molecules in the outer layer, nor any enrichment in the inner layer. This suppression of the concentration gradient between the internal and external environments confirms that the topological structure constructed by the multi-segment coordination extrusion process plays a physical anchoring role. The large-volume framework of tetramethyltetravinylcyclotetrasiloxane, after in-situ grafting, forms dense steric hindrance, fixing the polar byproducts produced by the decomposition of dicumyl peroxide in the molecular gaps of the cross-linked network of the insulation layer, fundamentally restricting the long-distance diffusion freedom of polar molecules in the polymer matrix.

[0072] The comparative data clearly reflect the thermal migration pathways of matter after the absence of the spatial locking mechanism. In Comparative Example 2, due to the lack of tetramethyltetravinylcyclotetrasiloxane, a large amount of acetophenone and cumyl alcohol in the outer layer evaporated and dissipated, with their contents decreasing to 812.4 ppm and 1205.7 ppm, respectively. However, in the inner layer, due to hindered volatilization and the continuous penetration of polar molecules towards the cable core, the contents surged to more than three times that of the outer layer. This indicates that the free volume of conventional polyethylene cannot restrict molecular movement under alternating thermal stress. In Comparative Examples 1 and 4, even without tetrabutyl titanate or N,N'-m-phenylenebismaleimide, significant byproduct retention and enrichment still occurred in the inner insulation layer. From an engineering perspective, the Lewis acid-base coordination network failed to be effectively established in the initial stage of extrusion, causing the subsequently injected tetramethyltetravinylcyclotetrasiloxane to remain outside the main chain. The final crosslinking network, due to its loose nodes, was unable to prevent the penetration of polar substances.

[0073] The disruption of the microscopic integrity of the cross-linked network caused by altering the basic feeding sequence is also reflected in the data. In Comparative Example 3, the materials were mixed and processed in a single step. Early-stage local cross-linking resulted in phase separation regions with uneven structural density. Polar byproducts continued to diffuse into the inner layer along the low-resistance channels formed by these network defects. Simply mixing sterically hindered monomers into polyethylene cannot spontaneously form a uniform barrier network. It is necessary to rely on a synergistic process of pre-coordination in the first stage and forced mixing and grafting in the second stage to lock the target macromolecular network at the mesoscopic scale, thereby cutting off the migration path of polar molecules to the internal signal transmission unit interface and ensuring the high-frequency electrical purity of the composite cable under complex operating conditions.

[0074] Test Example 3: Experimental steps: 1. Preparation of experimental subjects: The finished composite cross-linked polyethylene insulated cables prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were selected as experimental subjects.

[0075] 2. A gel content test was performed. The outer semiconductive shielding layer of the cable was peeled off, and the inner composite core and inner semiconductive shielding layer were removed. The cross-linked polyethylene insulation layer between the inner and outer semiconductive shielding layers was cut off. A fragment sample of approximately 0.500 grams of this insulation layer was cut and its initial mass was recorded. The sample was placed in a 120-mesh stainless steel mesh bag and refluxed in xylene solvent at 140°C for 12 hours. After extraction, the residue was dried to constant weight in a vacuum drying oven at 110°C, and the mass of the insoluble matter was weighed. The gel content was calculated as a percentage of the insoluble matter mass divided by the initial mass, thus characterizing the mass fraction of polyethylene macromolecules that had cross-linked to form a three-dimensional network structure.

[0076] 3. Conduct thermal elongation performance testing. Referring to GB / T 2951 standard, cut dumbbell-shaped test pieces of uniform thickness longitudinally from the insulation layer of each cable group. Mark a 20 mm interval in the middle of the test piece as the initial gauge length. .

[0077] 4. Suspend the test piece in a constant temperature oven at 200℃ and attach a counterweight to the lower end of the test piece so that the mechanical stress on the test piece is constant at 0.2MPa.

[0078] 5. Maintain a constant temperature load at 200℃ for 15 minutes, and use a steel ruler to measure the tensile distance between the two marks on the specimen. The counterweights were then removed, and the test piece was left in the oven to recover freely for 5 minutes. It was then removed and cooled to room temperature until the deformation stabilized. The remaining distance between the marks was measured again. .

[0079] 6. Calculate the thermal elongation and permanent deformation rate according to the formula: ; .

[0080] Experimental results (see Table 3): Table 3: Results of Crosslinking Degree and Heat Resistance Creep Properties for Each Experimental Group

[0081] Test conclusion: According to Table 3 and Figure 4 The data shows that the gel content in Examples 1 to 3 was all above 84%, and the thermal elongation at 200°C remained between 64.8% and 72.5%. In the research and development of conventional cross-linked polyethylene, the addition of liquid components often leads to a decrease in the high-temperature deformation resistance of the material due to the increase in molecular free volume. However, the results of this experiment show that after introducing tetramethyltetravinylcyclotetrasiloxane, the creep resistance of the insulating layer is better than that of ordinary cross-linked materials. This proves that the bulk component does not exist in a free state, but substantially participates in chemical cross-linking. Through the Lewis acid-base coordination center established in the first stage, tetramethyltetravinylcyclotetrasiloxane is locked in advance; subsequently, under the initiation of free radicals, the vinyl groups on its molecules form covalent bonds with the polyethylene backbone, constructing a high-functionality cross-linking node containing a rigid siloxane backbone, thereby microscopically restricting the thermal sliding of the macromolecular chain segments.

[0082] Observing the data evolution of the comparative examples reveals the importance of each component in constructing the composite network. Comparative Example 2, without the addition of siloxane components, showed a thermal elongation of 88.3%, falling within the performance range of standard cross-linked polyethylene. When tetrabutyl titanate (Comparative Example 1) or N,N'-m-phenylenebismaleimide (Comparative Example 4) was absent, the gel content of the insulating layer dropped below 80%, while the thermal elongation increased to 114.6% and 122.3%, respectively. This performance difference indicates that the lack of front-end coordination constraints leads to uneven distribution of the active components in the melt, failing to provide reinforcement and instead locally diluting the density of effective cross-linking points, resulting in a significantly accelerated elongation rate of the material under thermal load.

[0083] Furthermore, the impact of the process path on the integrity of the final cross-linked network was reflected in Comparative Example 3. Even with complete component proportions, the use of a one-time mixing and feeding process resulted in a gel content of only 74.8% in the insulation layer and a permanent deformation rate of 12.4%. This is because the uncontrollable early reactions during the extrusion stage consumed some of the peroxide, resulting in a lack of sufficient free radical concentration after entering the continuous vulcanization stage, leading to a large number of uncross-linked regions in the final molecular network. Under thermal stress, these chain segments undergo irreversible displacement, leading to structural instability. Therefore, ensuring the orderly occurrence of chemical reactions at predetermined nodes through the synergy of segmented feeding and temperature control is the physical basis for guaranteeing the mechanical dimensional stability of the composite cable insulation layer under complex operating thermal cycles.

[0084] Test Example 4: Experimental steps: 1. Preparation of experimental subjects: The finished composite cross-linked polyethylene insulated cables prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were selected as experimental subjects, and 50-meter-long cable samples were cut from each.

[0085] 2. Initial signal attenuation test: The initial signal attenuation constant of the un-thermally aged cable sample at 1 GHz was measured using a vector network analyzer. The vector network analyzer is a standard high-frequency electrical testing device. During the test, the transmission scattering parameters (S) at the 1 GHz center frequency were read. 21 The calculated power loss value is divided by the sample length of 0.05 km to obtain the initial signal attenuation constant, denoted as A0 (unit: dB / km).

[0086] 3. Place the cable samples that have completed the initial test in a constant temperature drying oven at 90℃ for 168 hours for accelerated thermal aging treatment. After taking them out, let them cool at room temperature for 24 hours.

[0087] 4. Dielectric loss test after aging: A 0.5 mm thick circular sample of the cross-linked polyethylene insulation layer between the inner and outer semiconductive shielding layers was cut from the aged cable sample. Using an impedance analyzer equipped with a high-frequency test fixture, the dielectric loss tangent (tanδ) of the insulation material at a frequency of 1 GHz was measured at an ambient temperature of 23 ± 2 ℃.

[0088] 5. Signal attenuation test after aging: Connect the 50-meter cable sample after aging to the vector network analyzer again, measure and calculate the signal attenuation constant after aging at 1GHz frequency according to the conventional method in step 2, and record it as A1.

[0089] 6. Calculation of attenuation increment after aging: The attenuation increment after aging for each group of samples is calculated according to the formula (A1-A0) / A0×100%. This increment data is used to directly characterize the degree of additional electromagnetic energy loss caused to high-frequency signal transmission due to the migration and enrichment of polar by-products inside the insulation layer when the cable is heated.

[0090] Experimental results (see Table 4): Table 4: Test results of high-frequency dielectric properties and signal attenuation for each experimental group

[0091] Test Conclusion According to Table 4 and Figure 5 The test results show that after 168 hours of thermal aging, the dielectric loss tangent of the insulation layer of the cables in Examples 1 to 3 is less than 4.5 × 10⁻⁶. -4 Furthermore, the signal attenuation increment is controlled within 2.5%. When high-frequency electromagnetic waves propagate inside the cable, polar molecules in the insulating medium undergo dipole orientation polarization with the high-frequency alternating electric field. The resulting internal friction is the main physical cause of signal energy attenuation. Combining the data on the radial distribution of polar molecules from the aforementioned test examples, it can be determined that this invention effectively limits the long-distance diffusion of highly polar byproducts such as acetophenone and cumyl alcohol produced by peroxide decomposition by constructing physical spatial steric hindrance in the polyethylene network using tetramethyltetravinylcyclotetrasiloxane. These polar molecules are fixed in situ and do not accumulate in large quantities at the interface near the internal signal transmission unit, thereby maintaining a stable high-frequency dielectric environment around the composite core and avoiding additional signal loss caused by the aging process.

[0092] The differences in the comparative data directly reflect the impact of the insulation layer's microstructure on macroscopic electrical purity. In Comparative Example 2, due to the absence of tetramethyltetravinylcyclotetrasiloxane, the polyethylene cross-linked network lacked sufficient spatial constraint, leading to a large accumulation of polar molecules in the inner layer under thermal stress at 90°C. This localized high concentration of dipoles resulted in an increase in its dielectric loss tangent to 14.52 × 10⁻⁶.-4 This resulted in a signal attenuation increase of up to 35.2% after aging. Comparative Examples 1 and 4, due to the absence of tetrabutyl titanate or N,N'-m-phenylenebismaleimide, failed to form effective Lewis acid-base coordination centers in the early stages. This led to the introduced tetramethyltetravinylcyclotetrasiloxane being either free outside the main chain network or unevenly distributed, failing to form a continuous physical barrier. Polar molecules penetrated these network defects and migrated into the inner layer, ultimately causing the attenuation increase to exceed 14% in both cases.

[0093] Improper processing sequence can also lead to degradation of electromagnetic transmission performance. Although Comparative Example 3 contained complete chemical components, the one-time mixing and feeding disrupted the sequence of in-situ anchoring and grafting, causing early local cross-linking and resulting in microscopic phase separation and network defects within the insulation layer. Polar substances continued to diffuse into the inner layer along these structurally uneven paths, with an aging attenuation increase of 18.4%. Experimental data show that simply mixing macromolecular monomers into polyethylene materials cannot spontaneously improve the high-frequency transmission environment. Only by relying on a two-stage temperature control and separation feeding process to ensure the uniform and complete establishment of a specific macromolecular topology network within the insulation layer can the enrichment path of cross-linking byproducts be effectively blocked in physical space, ensuring the signal transmission integrity of the composite cable under long-term heating conditions.

[0094] Test Example 5: Experimental steps: 1. Experimental Subject Preparation: The composite cross-linked polyethylene insulated cables prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were selected as the initial experimental subjects. A 500-meter length of each cable was cut as a sample. Each sample was then wound stress-free onto a standard test wooden reel with a bending radius greater than 20 times the cable's outer diameter. This standard test wooden reel is a standard cable winding and packaging carrier in the cable industry. Its function is to provide sufficient support radius, preventing macroscopic physical bending losses due to excessive bending, thereby eliminating interference from mechanical external forces on subsequent photoelectric test data.

[0095] 2. Initial optical attenuation test: The end of the cable sample coiled on the wooden reel is stripped to expose the integrated signal and power transmission composite core. Based on the physical structure of this composite core, the signal transmission carrier is identified, and the single-mode fiber inside is connected to an optical time-domain reflectometer. An optical pulse is emitted at a wavelength of 1550 nm, and the total optical power loss (dB) of the 500-meter sample is measured. This value is divided by the test length of 0.5 km, and the result is recorded as the initial optical attenuation before aging (unit: dB / km).

[0096] 3. Initial Eye Diagram Jitter Test: Under the same unaged condition, the high-frequency signal transmission carrier in the composite core is connected to a bit error rate tester and a broadband oscilloscope. A pseudo-random bit sequence (PRBS) at a rate of 10Gbps is injected through the bit error rate tester. The oscilloscope's built-in time analysis module is used to read the closure and offset of the signal eye diagram in the initial state, and the obtained values ​​are recorded as the initial 10Gbps eye diagram jitter value (unit: ps).

[0097] 4. High-temperature accelerated aging treatment: After all the initial signal tests mentioned above have been recorded, the cable samples coiled on wooden trays are pushed into a walk-in constant-temperature aging chamber. They are placed continuously at an ambient temperature of 90℃ for 720 hours to simulate the long-term heating conditions of cables in actual live-laid environments. After the aging cycle is completed, the samples are removed and allowed to stand at room temperature (20±5℃) for 48 hours to recover.

[0098] 5. Retesting signal performance after aging: Under the same instrument and environmental settings, repeat steps 2 and 3 on the aged cable to measure the optical attenuation constant and eye diagram jitter value after aging. Subtract the initial optical attenuation before aging from the optical attenuation constant after aging; the difference is recorded as the additional optical attenuation after aging. Subtract the initial 10Gbps eye diagram jitter value from the eye diagram jitter value after aging; the difference is recorded as the 10Gbps eye diagram jitter increment.

[0099] 6. Volume Swelling Rate Test of the Inner Semiconductor Shielding Layer: After completing all photoelectric tests, a 200mm short sample was cut from the middle of each group of 500-meter samples for physical dissection. The outer cross-linked polyethylene insulation layer was peeled off, and the tubular sample of the inner semiconductor shielding layer, which wraps around the composite wire core, was completely extracted. Using a high-precision digital micrometer with an accuracy of 0.001mm, the outer diameter and wall thickness of the semiconducting layer before and after aging were measured at the same cross-sectional position of the sample. The volume of the solid material was calculated using the formula for calculating the volume of a circular tube. The percentage increase in volume after aging was divided by the initial volume and recorded as the volume swelling rate of the inner semiconductor shielding layer. This quantifies the degree of swelling and erosion of the interface material caused by the inward migration of polar molecules in the outer insulation layer.

[0100] Experimental results (see Table 5): Table 5: Results of Semiconductor Layer Swelling Ratio and Signal Integrity Tests in Each Experimental Group

[0101] Test conclusion: According to Table 5 and Figure 6According to the data, after 720 hours of high-temperature thermal aging, the volume expansion rate of the inner semiconductive shielding layer of the cables in Examples 1 to 3 remained below 1.2%. Corresponding signal transmission tests showed that the additional optical attenuation at 1550nm wavelength was controlled within 0.015dB / km, and the eye diagram jitter increment of the 10Gbps high-speed signal did not exceed 2.1ps. In the material compatibility analysis of the optoelectronic composite cable, polar byproducts such as acetophenone and cumyl alcohol remaining in the insulation layer tended to migrate towards the lower-temperature inner side under long-term heating. The inner semiconductive shielding layer typically uses ethylene-vinyl acetate copolymer as the matrix, which has a high absorption affinity for polar organic matter. Once byproducts infiltrate and cause volume expansion of the semiconductive layer, the deformation generated by the expansion will squeeze the composite core inward. This mechanical squeezing not only applies radial stress to the optical fiber inside the stainless steel tube, causing micro-bending loss, but also changes the interface dielectric environment of the high-frequency data line, causing phase jitter. This solution grafts tetramethyltetravinylcyclotetrasiloxane nodes into the insulating layer formulation, utilizing their large-volume rigid framework to form a dense steric network within the polyethylene matrix. This microscopic physical constraint barrier locks polar molecules in situ within the insulating layer, cutting off their path to penetrate the semiconductive layer and preventing swelling and squeezing effects, thereby maintaining the long-term integrity of the underlying optical and electrical signals.

[0102] Observing the data from the comparative examples confirms the necessity of microstructure modification of the insulating matrix for preventing interface damage. In Comparative Example 2, due to the absence of tetramethyltetravinylcyclotetrasiloxane in the formulation, the conventional cross-linked network could not block the thermal diffusion of polar molecules. A large amount of peroxide decomposition products accumulated on the inner side, causing the swelling ratio of the inner semiconductive shielding layer to rise to 5.24%. Accompanied by this severe interface deformation, the signal carrier was subjected to both mechanical and electromagnetic interference, with its additional optical attenuation increasing to 0.165 dB / km and eye diagram jitter increment reaching 14.5 ps. In actual long-distance communication networks, this level of attenuation and phase degradation can easily lead to bit errors or even link interruptions at the receiver. In Comparative Examples 1 and 4, even without the pre-coordinated component, the swelling ratio of the shielding layer still exceeded 3.4%. This indicates that if the added bulk siloxane is not pre-anchored through Lewis acid-base interactions in the early stages of extrusion, it will undergo phase separation or agglomeration in the melt. The resulting localized dense areas cannot cover the voids in the overall network, and polar substances can still penetrate the inner layer along defect channels.

[0103] The impact of the timing of the processing and feeding steps on the density of the cross-linked network was evident in the tests of Comparative Example 3. Even with all chemical substances included, the early uncontrolled cross-linking reaction caused by a single-stage mixing and feeding disrupted the uniformity of the polymer network, resulting in an additional light attenuation of 0.112 dB / km after aging. Experimental data indicate that improving the long-term signal stability of composite cables requires not only the introduction of large-volume barrier materials but also the synergy of two-stage temperature control and a step-by-step feeding process. This process constraint ensures that functional monomers are uniformly distributed within the insulation material and undergo orderly chemical grafting, constructing a topological network without microscopic blind spots. This network, while meeting the mechanical and heat resistance requirements of the cable, prevents the penetration of cross-linking byproducts into the communication carrier interface from the source, ensuring the operational reliability of the composite cross-linked polyethylene insulated cable under complex electrically heated conditions.

[0104] 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 composite cross-linked polyethylene insulated cable integrating signal and power transmission, characterized in that, It includes, from the inside out, the following layers: composite wire core, inner semiconductive shielding layer, composite cross-linked polyethylene insulation layer, and outer semiconductive shielding layer; The composite cross-linked polyethylene insulation layer is made by extruding and cross-linking raw materials comprising the following parts by weight: 90-95 parts of low-density polyethylene granules, 5.42-11.6 parts of solid premix, and 0.7-2.0 parts of liquid co-solution. The solid premix contains N,N'-m-phenylenebismaleimide and tetrabutyl titanate, and the liquid co-solution contains tetramethyltetravinylcyclotetrasiloxane and dicumyl peroxide.

2. The composite cross-linked polyethylene insulated cable integrating signal and power transmission according to claim 1, characterized in that, The composite cross-linked polyethylene insulation layer is made from raw materials comprising the following parts by weight: 92 parts low-density polyethylene particles, 8.86 parts solid premix, and 1.2 parts liquid co-solution.

3. The composite cross-linked polyethylene insulated cable integrating signal and power transmission according to claim 1, characterized in that, The solid premix consists of the following components in parts by weight: 5-10 parts of low-density polyethylene powder, 0.1-0.5 parts of 4,4'-thiobis(6-tert-butyl-m-cresol), 0.3-1.0 parts of N,N'-m-phenylenebismaleimide, and 0.02-0.10 parts of tetrabutyl titanate.

4. The composite cross-linked polyethylene insulated cable integrating signal and power transmission according to claim 1, characterized in that, The liquid co-solution is composed of the following components in parts by weight: 0.2-0.8 parts of tetramethyltetravinylcyclotetrasiloxane and 0.5-1.2 parts of dicumyl peroxide.

5. A method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission, used to prepare the composite cross-linked polyethylene insulated cable integrating signal and power transmission as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Mix low-density polyethylene granules and solid premixed material evenly using a mixer to obtain the insulating base material to be processed; Step 2: Add the insulating base material to be processed into the main feed port of the twin-screw extruder, control the temperature of the first screw temperature zone to melt and plasticize, and obtain a plasticized melt containing a coordination network; Step 3: Using a liquid metering pump, the liquid eutectic is injected at constant pressure into the second screw section of the extruder, and the temperature of this section is controlled to mix the mixture, thereby obtaining a composite melt containing a pseudo-complex structure. Step 4: Introduce the composite melt into the three-layer co-extrusion die head, control the die head temperature, and use it as the insulation layer material to simultaneously coat the outer layer of the composite core with the inner semi-conductive shielding material melt and the outer semi-conductive shielding material melt, so that the composite melt is between the inner and outer semi-conductive shielding material melts, to obtain the cross-linked cable blank. Step 5: The cable blank to be cross-linked is fed into a continuous vulcanizing tube for step-by-step temperature cross-linking to obtain a composite cross-linked polyethylene insulated cable that has completed in-situ grafting and cross-linking. Step 6: After the composite cross-linked polyethylene insulated cable is cooled to room temperature through a water-cooling section, it is wound up.

6. The method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission according to claim 5, characterized in that, In step 1, the solid premix is ​​prepared in advance through the following steps: In a dry environment with relative humidity below 20%, low-density polyethylene powder is mixed with 4,4'-thiobis(6-tert-butyl-m-cresol) at 20-30°C to obtain a basic mixed powder. Subsequently, N,N'-m-phenylenebismaleimide and tetrabutyl titanate were added to the basic mixed powder, and the mixture was continued at 20-30°C to obtain a powdered solid premix.

7. The method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission according to claim 5, characterized in that, In step 3, the liquid co-solution is prepared in advance through the following steps: In a sealed mixing tank that has been purged with dry nitrogen, tetramethyltetravinylcyclotetrasiloxane is added and heated to 42-55°C to obtain a preheated crosslinking modifier. Dicumyl peroxide was added to the crosslinking modifier and stirred continuously until completely dissolved to obtain a transparent, homogeneous liquid eutectic.

8. The method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission according to claim 5, characterized in that, In step 2, the temperature of the first screw section of the twin-screw extruder is controlled at 90-110℃; in step 3, the temperature of the second screw section of the twin-screw extruder is controlled at 110-125℃; in step 4, the temperature of the three-layer co-extrusion die head is controlled at 125-135℃.

9. A method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission according to claim 5, characterized in that, In step 5, when the cable blank to be cross-linked is fed into the continuous vulcanizing tube, the pressure of the continuous vulcanizing tube is controlled to be 1.0-1.5 MPa.

10. The method for preparing a composite cross-linked polyethylene insulated cable integrating signal and power transmission according to claim 5, characterized in that, In step 5, the specific temperature control for the stepped temperature crosslinking is as follows: the temperature of the pre-crosslinking zone is set to 165-175℃, the temperature of the main crosslinking zone is set to 185-195℃, and the temperature of the deep crosslinking zone is set to 205-215℃.

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