A multi-layer flame-retardant heat-conducting cross-linked polyethylene cable structure and a preparation process thereof

Abstract

The application relates to the technical field of cables, and discloses a multilayer flame-retardant heat-conducting crosslinked polyethylene cable structure and a preparation process thereof. The product comprises, from inside to outside, a conductor layer, a heat-conducting flame-retardant buffer layer, a flame-retardant reinforcing linkage layer and an outer sheath layer, wherein the heat-conducting flame-retardant buffer layer contains a crosslinked polyethylene matrix, boron nitride, aluminum hydroxide and a shape memory polymer, and the outer surface is provided with interlocking protrusions with embedded heat-conducting microtubes; the flame-retardant reinforcing linkage layer contains a crosslinked polyethylene matrix, expanded graphite and graphene, and the inner surface is provided with grooves with flame-retardant elastic elements. The preparation method comprises the following steps: first, preparing a silver-plated conductor; then, respectively preparing the heat-conducting flame-retardant buffer layer and the flame-retardant reinforcing linkage layer; subsequently, aligning and hot-pressing the two layers to be combined; irradiating and crosslinking the combined structure; finally, extruding and coating the outer sheath, and cooling and shaping. The product can be used in new energy power stations, data centers and other scenes, and has the advantages of synergistic flame retardation and heat conduction and long-term stability of the interlayer structure.

Description

Technical Field

[0001] This application relates to the field of cable technology, and more specifically, to a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure and its manufacturing process. Background Technology

[0002] Cross-linked polyethylene (XLPE) cables, due to their excellent electrical insulation, mechanical strength, and resistance to environmental aging, have become core components of power transmission systems in critical fields such as new energy power plants, data centers, and rail transportation. In these scenarios, cables need to withstand high-load current transmission for extended periods. They must not only ensure stable insulation performance to avoid leakage risks but also efficiently dissipate the heat generated during conductor operation to prevent localized overheating and insulation aging. Simultaneously, they must possess reliable flame-retardant properties to address the risk of combustion caused by sudden events such as short circuits and overloads. Therefore, multilayer XLPE cables, combining high thermal conductivity, strong flame retardancy, and a stable interlayer structure, have become key products meeting the requirements of these scenarios.

[0003] However, existing multilayer flame-retardant and thermally conductive cross-linked polyethylene cables have significant limitations in their structural design: to achieve flame retardancy and thermal conductivity, they often employ a simple superposition of flame-retardant and thermally conductive layers, lacking a dedicated mechanical interlocking structure between the layers and relying solely on the adhesive bonding of the materials themselves. This results in low interlayer bonding strength, which easily leads to gaps due to thermal expansion and contraction during long-term operation, thereby increasing thermal resistance and hindering heat transfer. At the same time, the functional designs of the flame-retardant and thermally conductive layers are independent of each other, lacking a synergistic mechanism. This makes it impossible to optimize the heat conduction path and flame retardant effect through structural interaction under thermal stress conditions. Ultimately, it is difficult to simultaneously meet the requirements of interlayer bonding stability, low thermal resistance, and efficient flame retardant synergy, thus restricting the application of cables in high-reliability scenarios. Summary of the Invention

[0004] To address the problem that existing multilayer flame-retardant and thermally conductive cross-linked polyethylene cables cannot simultaneously achieve low thermal resistance and high flame retardancy, this application provides a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure and its manufacturing process.

[0005] In a first aspect, this application provides a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure, employing the following technical solution:

[0006] A multi-layer flame-retardant and thermally conductive cross-linked polyethylene cable structure, comprising, from the inside out, a conductor layer, a thermally conductive and flame-retardant buffer layer, a flame-retardant and reinforced linkage layer, and an outer sheath layer.

[0007] The thermally conductive and flame-retardant buffer layer is made of a material comprising the following components: 60-70 parts by weight of cross-linked polyethylene matrix, 15-20 parts by weight of boron nitride, 10-15 parts by weight of aluminum hydroxide, and 5-8 parts by weight of shape memory polymer; the outer surface of the thermally conductive and flame-retardant buffer layer is provided with interlocking protrusions, the interlocking protrusions are embedded with thermally conductive microtubes, and the sidewalls of the interlocking protrusions are provided with micropores;

[0008] The flame-retardant reinforced linkage layer is made of a material comprising the following components: 65-75 parts by weight of cross-linked polyethylene matrix, 10-15 parts by weight of expanded graphite and 5-10 parts by weight of graphene; the inner surface of the flame-retardant reinforced linkage layer is provided with a groove that matches the shape of the interlocking protrusion, and a flame-retardant elastic element is provided in the groove.

[0009] By employing the above technical solution, boron nitride in the thermally conductive and flame-retardant buffer layer is used to directionally conduct the heat generated during conductor operation; aluminum hydroxide is used to decompose and absorb heat during local overheating, providing initial flame retardancy; shape memory polymer is configured to deform under thermal stress, thereby driving the interlocking protrusions to displace. The interlocking protrusions and the grooves of the flame-retardant reinforced linkage layer are designed to enhance the mechanical bonding tightness of the two-layer structure; the thermally conductive microtubes embedded inside the interlocking protrusions are used to enhance the efficiency of heat transfer axially to the flame-retardant reinforced linkage layer; the micropores on the sidewalls of the interlocking protrusions provide channels for the flame-retardant elastic element to release its internal substances when compressed or heated. The expanded graphite in the flame-retardant reinforced linkage layer is used to expand and form a heat-insulating carbon layer when heated to block flame spread; graphene is used to construct a two-dimensional thermally conductive network to rapidly diffuse the heat transferred by the thermally conductive microtubes; the flame-retardant elastic element set in the groove is used to release the flame-retardant material it contains when compressed by the interlocking protrusions or when the ambient temperature rises. The components and structure work synergistically to achieve a combination of flame retardant and thermal conductivity functions, as well as long-term stability of the interlayer structure. The shape memory polymer can be selected from polyurethane-based or styrene-based shape memory polymers, with a trigger transition temperature at least 20°C higher than the rated operating temperature of the cable and lower than the decomposition temperature of cross-linked polyethylene. The micropores have a pore size of 10-100 micrometers and are configured to provide a release channel for magnesium hydroxide powder or other flame retardant decomposition products in the flame retardant elastic element when the interlocking protrusions are driven by thermal stress to squeeze the flame retardant elastic element, allowing them to penetrate to the interlayer interface and enhance the flame retardant effect. The thermally conductive medium is a highly thermally conductive silicone oil or liquid metal with good insulation properties, such as methyl silicone oil or phenyl silicone oil, with a filling amount of 80%-90% of the volume of the thermally conductive microtubes. The interlocking protrusions are circumferentially and uniformly distributed on the outer surface of the thermally conductive and flame-retardant buffer layer. The cross-linked polyethylene matrix is ​​high-density polyethylene with a melt flow rate of 2.1 g / 10 min and a density of 0.95 g / cm³.

[0010] Preferably, the conductor layer is a silver-plated copper conductor, and the thickness of the silver plating layer is 0.05-0.1 mm.

[0011] By adopting the above technical solution, using silver-plated copper conductors in the conductor layer, the copper substrate itself possesses excellent conductivity, playing a fundamental role in ensuring stable current transmission. The surface silver plating layer significantly reduces the contact resistance of the conductor surface, reducing energy loss during current transmission. Simultaneously, the silver plating layer forms a dense protective film, isolating the copper substrate from external moisture and corrosive impurities, thus inhibiting oxidation and rusting of the copper substrate and extending the conductor's service life. The silver plating layer thickness of 0.05-0.1mm ensures sufficient coverage of the copper substrate surface for resistance reduction and corrosion prevention, while avoiding excessively thick plating layers that could lead to high material costs or reduced overall conductor flexibility. This achieves a balance between current transmission efficiency, corrosion resistance, and practical economy. Furthermore, the silver plating layer reduces the skin effect during current transmission, resulting in more uniform current distribution and further reducing conductor power loss, especially in high-frequency current transmission scenarios.

[0012] Preferably, the flame-retardant elastic element is a composite structure formed by silicone rubber encapsulating magnesium hydroxide, wherein the mass percentage content of magnesium hydroxide is 30%-40%.

[0013] By adopting the above technical solution, the flame-retardant elastic component utilizes a composite structure of silicone rubber encapsulating magnesium hydroxide. Silicone rubber itself possesses excellent elasticity and aging resistance, serving to fix the magnesium hydroxide and prevent it from scattering during cable operation. It also deforms under interlocking protrusion compression, providing the power for the release of magnesium hydroxide. Furthermore, it can adapt to thermal expansion and contraction during long-term cable use, preventing the elastic component from cracking and failing. The encapsulated magnesium hydroxide, as a flame-retardant component, decomposes and absorbs heat when heated, generating flame-retardant substances such as magnesium oxide, which inhibits flame spread and reduces combustion intensity. The 30%-40% magnesium hydroxide mass ratio ensures that the elastic component contains sufficient flame-retardant components to meet flame-retardant requirements, while avoiding the problem of decreased silicone rubber elasticity and inability to achieve compression deformation due to excessive magnesium hydroxide content. This achieves a flame-retardant elastic component that combines reliable flame-retardant performance with durable structural elasticity, stably adapting to interlayer mechanical linkages.

[0014] Secondly, this application provides a manufacturing process for a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure, employing the following technical solution:

[0015] A manufacturing process for a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure includes the following steps:

[0016] S1. Preparation of conductor layer: Silver plating is performed on copper material, with the silver plating temperature controlled at 50-60℃ and the silver plating time at 30-40 minutes. Then, the conductor with the required cross-section is formed by drawing process.

[0017] S2. Preparation of thermally conductive and flame-retardant buffer layer: Add 60-70 parts by weight of cross-linked polyethylene resin, 15-20 parts by weight of boron nitride powder, 10-15 parts by weight of aluminum hydroxide powder and 5-8 parts by weight of shape memory polymer particles to a high-speed mixer and mix at 80-100℃ for 5-15 minutes to obtain mixture A; use an extruder to extrude mixture A at 120-160℃, and simultaneously embed pre-prepared thermally conductive microtubes during the extrusion process, and form a thermally conductive and flame-retardant buffer layer with interlocking protrusions and micropores through die forming, with an extrusion speed of 10-20m / min;

[0018] S3. Preparation of flame-retardant reinforced linkage layer: Add 65-75 parts by weight of cross-linked polyethylene resin, 10-15 parts by weight of expanded graphite and 5-10 parts by weight of graphene to a high-speed mixer and mix at 70-90℃ for 8-12 minutes to obtain mixture B; use an extruder to extrude mixture B at 130-170℃, and simultaneously form grooves through a die at an extrusion speed of 8-15m / min, and immediately fill the grooves with flame-retardant elastic elements after the grooves are formed;

[0019] S4. Composite treatment: Align the thermally conductive and flame-retardant buffer layer with interlocking protrusions prepared in step S2 with the flame-retardant reinforced linkage layer with grooves and flame-retardant elastic elements prepared in step S3, and composite it through a hot pressing process. The composite temperature is 140-180℃, so that the interlocking protrusions are embedded in the grooves and in contact with the flame-retardant elastic elements.

[0020] S5. Crosslinking treatment: The composite structure is subjected to irradiation crosslinking with an irradiation dose of 5-15 MGAy and an irradiation time of 20-40 minutes.

[0021] S6. Preparation of outer sheath layer: Low smoke halogen-free flame retardant material is extruded at 150-190℃ and coated on the cross-linked flame retardant and reinforced linkage layer. The extrusion speed is 12-22m / min. After cooling and shaping, the finished cable is obtained.

[0022] By adopting the above technical solution, step S1 ensures a uniform and dense silver plating layer by controlling the silver plating temperature and time, and guarantees the accuracy of the conductor cross-section in conjunction with the drawing process, providing a stable foundation for subsequent layer coating; step S2 ensures full dispersion of each component by precisely controlling the mixing temperature and time, and simultaneously embeds heat-conducting microtubes and forms interlocking protrusions and micropores during extrusion, avoiding damage to the structure during post-processing and ensuring the integrity of the buffer layer's functional structure; step S3 optimizes the mixing parameters to ensure uniform distribution of the flame-retardant reinforcing material, and immediately fills the grooves with elastic elements after the grooves are formed to ensure a tight fit between the two, laying the structural foundation for interlayer linkage; step S4 hot-pressing composite ensures precise fitting of the interlocking protrusions and grooves, enhancing the interlayer bonding strength; step S5 irradiation crosslinking improves the overall stability and mechanical properties of the material; step S6 extrudes the outer sheath and cools and shapes it to form complete protection. The matching of parameters and the seamless operation of each step ensure the precision of each layer's structure, the effective functioning of the components, and the strong interlayer bonding, thereby enabling the prepared cable to stably achieve the synergistic effect of flame retardancy and thermal conductivity.

[0023] Preferably, in step S2, the heat-conducting microtube is made of copper, with an inner diameter of 0.5-1 mm and a wall thickness of 0.1-0.2 mm. The heat-conducting microtube has a closed structure and is filled with a heat-conducting medium.

[0024] By adopting the above technical solution, the heat-conducting microtubes are made of copper, utilizing copper's excellent thermal conductivity to rapidly conduct heat. The 0.5-1mm inner diameter provides sufficient space for the internal heat-conducting medium while avoiding excessive diameter that could compromise the structural strength of the interlocking protrusions. The 0.1-0.2mm wall thickness ensures the microtube's structural stability and prevents deformation, while minimizing obstruction to heat transfer. The sealed structure prevents leakage of the heat-conducting medium and ensures long-term effective heat conduction, while the internal heat-conducting medium enhances the uniformity of heat transfer. Thus, the heat-conducting microtubes achieve both efficient heat conduction and compatibility with the interlocking protrusion structure, maintaining long-term thermal stability.

[0025] Preferably, in step S3, the method for preparing the flame-retardant elastic component is as follows: 60-70 parts by weight of silicone rubber and 30-40 parts by weight of magnesium hydroxide powder are mixed, kneaded, and molded, and then vulcanized at a temperature of 110-130°C for 10-20 minutes to obtain the flame-retardant elastic component.

[0026] By adopting the above technical solution, mixing silicone rubber and magnesium hydroxide in a certain proportion and then kneading, magnesium hydroxide can be uniformly dispersed in the silicone rubber matrix, avoiding the problem of insufficient local flame retardant effect or uneven elasticity of elastic parts caused by magnesium hydroxide agglomeration. The subsequent molding process can make the elastic part form a shape that fits the groove, ensuring that it can fit tightly against the inner wall of the groove after filling. The vulcanization temperature of 110-130℃ can ensure that the silicone rubber is fully cross-linked to form a stable elastic structure, avoiding incomplete vulcanization and insufficient elasticity due to too low a temperature, and also preventing the silicone rubber from aging and becoming brittle due to too high a temperature. The vulcanization time of 10-20 minutes further ensures that the vulcanization reaction is sufficient and efficient, avoiding incomplete vulcanization due to too short a time and increased energy consumption or deterioration of material properties due to too long a time. The resulting flame-retardant elastic component possesses both the good elasticity of silicone rubber to adapt to the extrusion action of interlocking protrusions, and the ability to stably release flame-retardant components during extrusion due to the uniform distribution of magnesium hydroxide. Simultaneously, its stable elastic structure can withstand the thermal expansion and contraction during long-term cable operation, thus providing a reliable elastic flame-retardant component for the synergistic effect of interlayer flame retardancy and thermal conductivity. Methyl vinyl silicone rubber is preferred as the silicone rubber to ensure processing fluidity and finished product elasticity. The magnesium hydroxide powder has a particle size of 1-5 μm and is pre-treated to remove adsorbed water and prevent air bubbles from forming during mixing. Specifically, the silicone rubber and magnesium hydroxide powder are mixed. The methyl vinyl silicone rubber is first placed in a two-roll mill and plasticized at 60°C and a roll gap of 2 mm for 10 minutes until fully softened, during which internal air bubbles are removed. Magnesium hydroxide powder is dried at 120℃ for 3 hours to remove adsorbed water. Then, it is added to the plasticized silicone rubber in batches, with each batch not exceeding 1 / 5 of the silicone rubber mass. The roller gap of the open mill is then adjusted to 0.5-1mm, and the mixture is repeatedly mixed for 40 minutes with multiple turnings until there are no obvious particles on the cross-section of the mixture and magnesium hydroxide is evenly dispersed in the silicone rubber. The mixture is then transferred to a mold that matches the shape of the groove of the flame-retardant reinforced linkage layer. The mold is preheated to 100℃ and the cavity surface is coated with a special release agent for silicone rubber. The mold is then placed in a flat vulcanizing machine and vulcanized for 10-20 minutes at a temperature of 110-130℃ and a pressure of 10-15MPa. After vulcanization, the mold is demolded and the molded part is cooled to room temperature to obtain a flame-retardant elastic part.

[0027] Preferably, in step S4, the hot pressing process uses a pressure roller device with a matching convex and concave structure, the pressure roller temperature is 140-180℃, and the pressure is 0.5-2.0MPa.

[0028] By employing the above technical solution, and utilizing a pressure roller device with a matching convex and concave structure in the hot-pressing process, the interlocking protrusions of the thermally conductive and flame-retardant buffer layer and the groove shape of the flame-retardant reinforcing linkage layer can be precisely matched. This avoids interlayer misalignment and ensures precise fitting of the protrusions and grooves, preventing the linkage function from failing under subsequent thermal stress due to alignment deviations. The pressure roller temperature of 140-180℃ moderately softens the cross-linked polyethylene substrate, enhancing the fluidity and interface adhesion of the interlayer materials and improving the interlayer bonding strength, while preventing deformation or material degradation of the formed interlocking protrusions and grooves due to excessive temperature. The pressure of 0.5-2.0MPa ensures that the interlocking protrusions are fully embedded in the grooves, ensuring close contact between the protrusions and the flame-retardant elastic element, thus solidifying the interlayer structure and reducing interlayer gaps, while preventing protrusion breakage or groove damage due to excessive pressure. This results in a strong and precise bond between the two layers after hot pressing, providing a stable structural foundation for the interlayer mechanical linkage under thermal stress during subsequent cable operation, ensuring the synergistic effect of flame retardancy and thermal conductivity.

[0029] Preferably, in step S5, the irradiation crosslinking is performed using an electron accelerator with an electron energy of 1-3 MeV.

[0030] By adopting the above technical solution and using an electron accelerator for irradiation crosslinking, the electron accelerator, with its high dose rate, controllable irradiation energy, and uniform effect, can rapidly act on the multi-layered composite structure, avoiding the low efficiency and uneven irradiation problems of traditional irradiation methods. This improves the efficiency of crosslinking processing and ensures that each layer of material receives stable irradiation. The electron energy of 1-3 MeV ensures that electrons can effectively penetrate the composite structure composed of the thermally conductive and flame-retardant buffer layer and the flame-retardant reinforcing linkage layer, allowing the crosslinked polyethylene matrix in both layers to fully undergo the crosslinking reaction and form a stable three-dimensional network structure. This improves the overall mechanical strength, heat deformation resistance, and long-term aging resistance of the material. It also avoids the problems of insufficient crosslinking and insufficient structural strength in the inner layer due to too low electron energy, or degradation of the surface material and decreased electrical insulation performance due to too high energy. Ultimately, this achieves a composite structure with uniform and sufficient crosslinking, stable overall performance, and the ability to withstand thermal and mechanical stresses during long-term cable operation.

[0031] Preferably, in step S6, the low-smoke halogen-free flame retardant material is composed of the following components: 50-60 parts by weight of polyolefin, 20-30 parts by weight of aluminum hydroxide, 5-10 parts by weight of magnesium hydroxide and 3-5 parts by weight of lubricant.

[0032] By adopting the above technical solution, polyolefin is used as the matrix in the low-smoke halogen-free flame-retardant material, providing the outer sheath with basic mechanical strength and flexibility. This ensures the outer sheath can withstand the mechanical stress during cable laying and operation. Aluminum hydroxide and magnesium hydroxide, as flame-retardant components, decompose and absorb heat when heated, generating a flame-retardant oxide layer that inhibits flame spread and reduces smoke release, meeting the environmental requirements of low-smoke halogen-free. The lubricant improves the material's flowability during extrusion, avoiding processing difficulties caused by a high proportion of inorganic flame retardants, ensuring smooth extrusion and a smooth surface of the outer sheath. The proportions of each component are well-balanced, enabling the outer sheath to provide reliable flame-retardant protection and low-smoke properties, while also possessing good processing performance and mechanical protection capabilities, thus providing stable outer protection for the entire cable.

[0033] Preferably, in step S6, the cooling and shaping process uses water cooling, with a cooling water temperature of 20-30℃ and a cooling time of 5-10 minutes.

[0034] By adopting the above technical solution, water cooling is used for cooling and shaping. Water has high heat exchange efficiency and can quickly absorb the residual heat after the outer sheath is extruded, which accelerates the material curing and prevents the outer sheath from shrinking or deforming due to slow cooling. At the same time, rapid water cooling ensures that the outer sheath adheres tightly to the flame-retardant reinforced interlayer before shrinkage, avoiding interlayer gaps caused by the shrinkage of the outer sheath due to slow cooling. This ensures that the outer sheath can effectively transfer and disperse external mechanical stress, protecting the inner structure. The cooling water temperature of 20-30℃ ensures sufficient cooling speed to fix the shape of the outer sheath, while avoiding excessively low water temperature that could cause internal stress, cracking, or warping due to excessively high water temperature, and also prevents excessively high water temperature from prolonging the cooling time and affecting production efficiency. The cooling time of 5-10 minutes ensures that the outer sheath is fully cooled and shaped from the surface to the inner layer, ensuring its dimensional accuracy and structural stability. This allows the outer sheath to stably maintain its designed shape, tightly covering the flame-retardant reinforced interlayer, and providing reliable mechanical protection and flame-retardant assistance.

[0035] In summary, this application has the following beneficial effects:

[0036] 1. Because this application uses a thermally conductive and flame-retardant buffer layer composed of cross-linked polyethylene matrix and boron nitride aluminum hydroxide shape memory polymer, and a flame-retardant and reinforced linkage layer composed of cross-linked polyethylene matrix and expanded graphene, and sets interlocking protrusions with thermally conductive microtubes and grooves with flame-retardant elastic elements to interlock with each other to form a mechanical interlocking interface, the technical effect of significantly improving interlayer bonding strength and significantly reducing thermal resistance is achieved, realizing the synergistic enhancement of thermal conductivity and flame retardant function.

[0037] 2. In this application, silver-plated copper conductor is preferably used as the cable conductor layer, and a composite structure with a specific content of magnesium hydroxide is formed by encapsulating it with silicone rubber as a flame-retardant elastic element. Since the silver plating layer improves the conductor's oxidation resistance and conductivity stability, and the elastic flame-retardant structure provides both flame-retardant and buffering functions in the mechanical interlocking interface, the overall electrical performance and long-term flame-retardant stability of the cable are improved.

[0038] 3. The method of this application involves simultaneously embedding heat-conducting microtubes and forming interlocking protrusions in the mold during the extrusion process, simultaneously forming grooves and filling them with flame-retardant elastic elements during the extrusion of the flame-retardant reinforcing layer, and then achieving mechanical interlocking composite of the two layers through a hot pressing process. Finally, the product is cross-linked and shaped by irradiation, thus obtaining a cable product with precise alignment of each functional layer structure, tight interface bonding, and stable performance. Attached Figure Description

[0039] Figure 1 This is a three-dimensional schematic diagram of a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure provided in this application;

[0040] Figure 2 This is a schematic diagram of the micropores in a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure provided in this application;

[0041] Figure 3 This is a planar schematic diagram of a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure provided in this application;

[0042] Figure 4 This is a flowchart of the manufacturing process of a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure provided in this application.

[0043] Among them, 1. Conductor layer; 2. Thermally conductive and flame-retardant buffer layer; 201. Interlocking protrusion; 202. Thermally conductive microtube; 203. Micropore; 3. Flame-retardant and reinforced linkage layer; 301. Groove; 302. Flame-retardant elastic element; 4. Outer sheath layer. Detailed Implementation

[0044] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0045] Technical concept:

[0046] In scenarios such as new energy power plants and data centers where the flame retardancy and thermal conductivity of cables are stringent, existing multilayer flame-retardant and thermally conductive cross-linked polyethylene cable technology has significant limitations: On the one hand, the interlayer is mostly simply stacked or co-extruded, lacking a dedicated mechanical interlocking structure, relying only on the adhesive bonding of the material itself. During long-term operation, gaps are easily generated due to thermal expansion and contraction, leading to increased thermal resistance and hindered heat transfer; on the other hand, the flame retardant function and the thermal conductivity function are designed independently. The flame retardant layer relies only on passive heat insulation, and the thermal conductivity layer relies only on a single medium for temperature transfer. No functional linkage mechanism under thermal stress has been established, and in some solutions, the flame retardant is prone to agglomeration and the heat conduction path is not continuous.

[0047] Structurally, this technical solution employs a multi-layer architecture comprising a conductor layer, a thermally conductive and flame-retardant buffer layer, a flame-retardant reinforced linkage layer, and an outer sheath layer. The thermally conductive and flame-retardant buffer layer features interlocking protrusions with thermally conductive microtubes and micropores, while the flame-retardant reinforced linkage layer incorporates adapting grooves with flame-retardant elastic components, forming a stable mechanical interlocking interface. In terms of materials, the thermally conductive and flame-retardant buffer layer utilizes a composite of boron nitride with directional thermal conductivity, aluminum hydroxide providing initial flame retardancy, and a shape memory polymer capable of thermal drive. The flame-retardant reinforced linkage layer uses a composite of expandable and thermally insulating expanded graphite and highly thermally conductive graphene. The flame-retardant elastic component is made of silicone rubber encapsulating magnesium hydroxide, combining elasticity and flame retardancy, achieving complementary material functions. In terms of process, temperature and time are controlled during the conductor silver plating process to ensure conductivity and corrosion resistance. Copper thermally conductive microtubes are simultaneously embedded during the extrusion of the thermally conductive and flame-retardant buffer layer to prevent structural damage. After the grooves in the flame-retardant reinforced linkage layer are formed, flame-retardant elastic components are immediately filled to ensure tight adhesion. Hot-pressing composite ensures strong interlayer bonding, and irradiation cross-linking enhances the overall stability of the material.

[0048] Preparation Example 1

[0049] The preparation method of shape memory polymer particles is as follows:

[0050] Take 50 parts by weight of low-density polyethylene, 45 parts by weight of polycaprolactone, 12 parts by weight of maleic anhydride-grafted polyethylene, and 2 parts by weight of antioxidant 1010. Place the above raw materials in a vacuum drying oven and dry at 90°C for 3 hours to remove moisture. Then, add the dried raw materials to a twin-screw extruder, control the screw speed at 220 rpm, and set the temperatures of each zone of the extruder to 160°C, 170°C, 180°C, and 175°C respectively. Melt-blend for 10 minutes to fully disperse and blend the components. Extrude the blended melt through the extruder die and cut it into particles with a particle size of 2-5 mm by a water-cooled pelletizer. Then, place the particles in a 70°C forced-air drying oven and dry for 2 hours to remove surface moisture. The resulting shape memory polymer particles are the desired shape memory polymer particles. These particles can undergo a deformation rate of 15%-20% at 60-80°C and do not agglomerate after mixing with the cross-linked polyethylene matrix, thus stably performing the thermally driven deformation function.

[0051] Preparation Example 2

[0052] The fabrication method of thermally conductive microtubes is as follows:

[0053] A 5mm diameter T2 copper rod is cold-drawn in multiple passes using an LG-20 cold drawing machine. The first pass uses a 3mm die, and the die diameter decreases by 0.2mm for each subsequent pass, resulting in a copper tube with an inner diameter of 0.5-1mm and a wall thickness of 0.1-0.2mm. The copper tube is then cut into 500mm long sections, and the ends are welded using an HL-100 fiber laser welding machine with a welding spot diameter of 0.2mm and a welding speed of 1mm / s. The sealed copper tube is then evacuated to -0.09MPa, and a heat-conducting medium is injected under vacuum. Once the medium fills 80%-90% of the volume, the injection port is welded again to obtain the heat-conducting microtube.

[0054] The following are the main raw materials and reagents used in the preparation examples, embodiments, and comparative examples, and their sources and specifications are as follows; unless otherwise specified, all reagents are commercially available analytical grade or higher products:

[0055] Low-density polyethylene: purchased from Haozheng New Material Technology (Dongguan) Co., Ltd., grade 722.

[0056] 2. Polycaprolactone: Purchased from Shanghai Yuanye Biotechnology Co., Ltd., brand name S26795.

[0057] 3. Maleic anhydride-grafted polyethylene: purchased from Shanghai Koraman Reagent Co., Ltd., brand: Kramar.

[0058] 4. Antioxidant 1010: Purchased from Shanghai Yuanye Biotechnology Co., Ltd., brand name S67391.

[0059] 5. Methyl vinyl silicone rubber: purchased from Chongqing Ruiya Biotechnology Co., Ltd., CAS: 67762-94-1.

[0060] 6. Polyolefin: Purchased from Dongguan Shunying Plastic Raw Materials Co., Ltd., brand name AV161.

[0061] 7. Lubricant: Purchased from Shanghai Lawen New Material Technology Co., Ltd., item number: EBS10.

[0062] 8. Cross-linked polyethylene matrix: purchased from Shenzhen Shenghang Plastics & Chemical Co., Ltd., item number: HFDK9253. Example

[0063] This application provides a multi-layer flame-retardant and thermally conductive cross-linked polyethylene cable structure, which includes, from the inside out, a conductor layer, a thermally conductive and flame-retardant buffer layer, a flame-retardant and reinforced linkage layer, and an outer sheath layer.

[0064] The thermally conductive and flame-retardant buffer layer is made of a material containing the following components: 65 parts by weight of cross-linked polyethylene matrix, 17.5 parts by weight of boron nitride, 12.5 parts by weight of aluminum hydroxide and 6.5 parts by weight of shape memory polymer; the outer surface of the thermally conductive and flame-retardant buffer layer is provided with interlocking protrusions, the interlocking protrusions are embedded with thermally conductive microtubes, and the sidewalls of the interlocking protrusions are provided with micropores.

[0065] The flame-retardant reinforced linkage layer is made of a material comprising the following components: 70 parts by weight of cross-linked polyethylene matrix, 12.5 parts by weight of expanded graphite and 7.5 parts by weight of graphene; the inner surface of the flame-retardant reinforced linkage layer is provided with a groove that matches the shape of the interlocking protrusion, and a flame-retardant elastic element is provided in the groove.

[0066] The conductor layer is a silver-plated copper conductor with a silver plating thickness of 0.075 mm.

[0067] The flame-retardant elastic component is a composite structure formed by silicone rubber encapsulating magnesium hydroxide, wherein the mass percentage content of magnesium hydroxide is 35%.

[0068] The manufacturing process of the above-mentioned multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure includes the following steps:

[0069] S1. Preparation of conductor layer: Silver plating is performed on copper material, with the silver plating temperature controlled at 55℃ and the silver plating time at 35 minutes. Then, the conductor with the required cross-section is formed by drawing process.

[0070] S2. Preparation of thermally conductive and flame-retardant buffer layer: 65 parts by weight of cross-linked polyethylene resin, 17.5 parts by weight of boron nitride powder, 12.5 parts by weight of aluminum hydroxide powder and 6.5 parts by weight of shape memory polymer particles are added to a high-speed mixer and mixed at 90°C for 10 minutes to obtain mixture A; mixture A is extruded at 140°C using an extruder, and pre-prepared thermally conductive microtubes are embedded simultaneously during the extrusion process. The thermally conductive and flame-retardant buffer layer with interlocking protrusions and micropores is formed by molding through a die at an extrusion speed of 15 m / min.

[0071] The heat-conducting microtube is made of copper, with an inner diameter of 0.75 mm and a wall thickness of 0.15 mm. The heat-conducting microtube has a closed structure and is filled with a heat-conducting medium.

[0072] S3. Preparation of flame-retardant reinforced linkage layer: 70 parts by weight of cross-linked polyethylene resin, 12.5 parts by weight of expanded graphite and 7.5 parts by weight of graphene are added to a high-speed mixer and mixed at 80°C for 10 minutes to obtain mixture B; mixture B is extruded at 150°C using an extruder, and grooves are simultaneously formed through a die at an extrusion speed of 11.5 m / min, and flame-retardant elastic elements are immediately filled after the grooves are formed;

[0073] The preparation method of the flame-retardant elastic component is as follows: 65 parts by weight of silicone rubber and 35 parts by weight of magnesium hydroxide powder are mixed, kneaded and molded, and then vulcanized at 120°C for 15 minutes to obtain the flame-retardant elastic component.

[0074] S4. Composite treatment: Align the thermally conductive and flame-retardant buffer layer with interlocking protrusions prepared in step S2 with the flame-retardant reinforced linkage layer with grooves and flame-retardant elastic elements prepared in step S3, and composite it through a hot pressing process at a composite temperature of 160°C, so that the interlocking protrusions are embedded in the grooves and in contact with the flame-retardant elastic elements.

[0075] The hot pressing process uses a pressure roller device with a matching convex and concave structure. The pressure roller temperature is 160℃ and the pressure is 1.25MPa.

[0076] S5. Crosslinking treatment: The composite structure is subjected to irradiation crosslinking with an irradiation dose of 10 MGry and an irradiation time of 30 minutes.

[0077] The irradiation crosslinking was carried out using an electron accelerator with an electron energy of 2 MeV.

[0078] S6. Preparation of outer sheath layer: Low smoke halogen-free flame retardant material is extruded at 170°C and coated on the outside of the cross-linked flame retardant and reinforced linkage layer. The extrusion speed is 17m / min. After cooling and shaping, the finished cable is obtained.

[0079] The low-smoke halogen-free flame retardant material is composed of the following components: 55 parts by weight of polyolefin, 25 parts by weight of aluminum hydroxide, 7.5 parts by weight of magnesium hydroxide and 4 parts by weight of lubricant.

[0080] The cooling and shaping process uses water cooling at a temperature of 25°C for 7.5 minutes. Example

[0081] This application provides a multi-layer flame-retardant and thermally conductive cross-linked polyethylene cable structure, which includes, from the inside out, a conductor layer, a thermally conductive and flame-retardant buffer layer, a flame-retardant and reinforced linkage layer, and an outer sheath layer.

[0082] The thermally conductive and flame-retardant buffer layer is made of a material containing the following components: 60 parts by weight of cross-linked polyethylene matrix, 15 parts by weight of boron nitride, 10 parts by weight of aluminum hydroxide and 5 parts by weight of shape memory polymer; the outer surface of the thermally conductive and flame-retardant buffer layer is provided with interlocking protrusions, the interlocking protrusions are embedded with thermally conductive microtubes, and the sidewalls of the interlocking protrusions are provided with micropores.

[0083] The flame-retardant reinforced linkage layer is made of a material containing the following components: 65 parts by weight of cross-linked polyethylene matrix, 10 parts by weight of expanded graphite and 5 parts by weight of graphene; the inner surface of the flame-retardant reinforced linkage layer is provided with a groove that matches the shape of the interlocking protrusion, and a flame-retardant elastic element is provided in the groove.

[0084] The conductor layer is a silver-plated copper conductor with a thickness of 0.05 mm; the flame-retardant elastic element is a composite structure formed by silicone rubber encapsulating magnesium hydroxide, wherein the mass percentage content of magnesium hydroxide is 30%.

[0085] The manufacturing process of the above-mentioned multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure includes the following steps:

[0086] S1. Preparation of conductor layer: Silver plating is performed on copper material, with the silver plating temperature controlled at 50℃ and the silver plating time at 30 minutes. Then, the conductor with the required cross-section is formed by drawing process.

[0087] S2. Preparation of thermally conductive and flame-retardant buffer layer: 60 parts by weight of cross-linked polyethylene resin, 15 parts by weight of boron nitride powder, 10 parts by weight of aluminum hydroxide powder and 5 parts by weight of shape memory polymer particles are added to a high-speed mixer and mixed at 80°C for 5 minutes to obtain mixture A; mixture A is extruded at 120°C using an extruder, and pre-prepared thermally conductive microtubes are embedded simultaneously during the extrusion process. The thermally conductive and flame-retardant buffer layer with interlocking protrusions and micropores is formed by molding through a die at an extrusion speed of 10 m / min.

[0088] The heat-conducting microtube is made of copper, with an inner diameter of 0.5 mm and a wall thickness of 0.1 mm. The heat-conducting microtube has a closed structure and is filled with a heat-conducting medium.

[0089] S3. Preparation of flame-retardant reinforced linkage layer: 65 parts by weight of cross-linked polyethylene resin, 10 parts by weight of expanded graphite and 5 parts by weight of graphene are added to a high-speed mixer and mixed at 70°C for 8 minutes to obtain mixture B; mixture B is extruded at 130°C using an extruder, and grooves are simultaneously formed through a die at an extrusion speed of 8 m / min, and flame-retardant elastic parts are immediately filled after the grooves are formed.

[0090] The method for preparing the flame-retardant elastic component is as follows: 60 parts by weight of silicone rubber and 40 parts by weight of magnesium hydroxide powder are mixed, kneaded and molded, and then vulcanized at 110°C for 10 minutes to obtain the flame-retardant elastic component.

[0091] S4. Composite treatment: Align the thermally conductive and flame-retardant buffer layer with interlocking protrusions prepared in step S2 with the flame-retardant reinforced linkage layer with grooves and flame-retardant elastic elements prepared in step S3, and composite it through a hot pressing process at a composite temperature of 140°C, so that the interlocking protrusions are embedded in the grooves and in contact with the flame-retardant elastic elements.

[0092] The hot pressing process uses a pressure roller device with a matching convex and concave structure. The pressure roller temperature is 140℃ and the pressure is 0.5MPa.

[0093] S5. Crosslinking treatment: The composite structure is subjected to irradiation crosslinking with an irradiation dose of 5 MGry and an irradiation time of 20 minutes.

[0094] The irradiation crosslinking was carried out using an electron accelerator with an electron energy of 1 MeV.

[0095] S6. Preparation of outer sheath layer: Low smoke halogen-free flame retardant material is extruded at 150°C and coated on the cross-linked flame retardant and reinforced linkage layer. The extrusion speed is 12m / min. After cooling and shaping, the finished cable is obtained.

[0096] The low-smoke halogen-free flame retardant material is composed of the following components: 50 parts by weight of polyolefin, 20 parts by weight of aluminum hydroxide, 5 parts by weight of magnesium hydroxide and 3 parts by weight of lubricant.

[0097] The cooling and shaping process uses water cooling at a temperature of 20°C for 5 minutes. Example

[0098] This application provides a multi-layer flame-retardant and thermally conductive cross-linked polyethylene cable structure, which includes, from the inside out, a conductor layer, a thermally conductive and flame-retardant buffer layer, a flame-retardant and reinforced linkage layer, and an outer sheath layer.

[0099] The thermally conductive and flame-retardant buffer layer is made of a material containing the following components: 70 parts by weight of cross-linked polyethylene matrix, 20 parts by weight of boron nitride, 15 parts by weight of aluminum hydroxide and 8 parts by weight of shape memory polymer; the outer surface of the thermally conductive and flame-retardant buffer layer is provided with interlocking protrusions, the interlocking protrusions are embedded with thermally conductive microtubes, and the sidewalls of the interlocking protrusions are provided with micropores.

[0100] The flame-retardant reinforced linkage layer is made of a material containing the following components: 75 parts by weight of cross-linked polyethylene matrix, 15 parts by weight of expanded graphite and 10 parts by weight of graphene; the inner surface of the flame-retardant reinforced linkage layer is provided with a groove that matches the shape of the interlocking protrusion, and a flame-retardant elastic element is provided in the groove.

[0101] The conductor layer is a silver-plated copper conductor with a thickness of 0.1 mm; the flame-retardant elastic element is a composite structure formed by silicone rubber encapsulating magnesium hydroxide, wherein the mass percentage content of magnesium hydroxide is 40%.

[0102] The manufacturing process of the above-mentioned multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure includes the following steps:

[0103] S1. Preparation of conductor layer: Silver plating is performed on copper material, with the silver plating temperature controlled at 60℃ and the silver plating time at 40 minutes. Then, the conductor with the required cross-section is formed by drawing process.

[0104] S2. Preparation of thermally conductive and flame-retardant buffer layer: 70 parts by weight of cross-linked polyethylene resin, 20 parts by weight of boron nitride powder, 15 parts by weight of aluminum hydroxide powder and 8 parts by weight of shape memory polymer particles are added to a high-speed mixer and mixed at 100°C for 15 minutes to obtain mixture A; mixture A is extruded at 160°C using an extruder, and pre-prepared thermally conductive microtubes are embedded simultaneously during the extrusion process. The thermally conductive and flame-retardant buffer layer with interlocking protrusions and micropores is formed by molding through a die at an extrusion speed of 20 m / min.

[0105] The heat-conducting microtube is made of copper, with an inner diameter of 1 mm and a wall thickness of 0.2 mm. The heat-conducting microtube has a closed structure and is filled with a heat-conducting medium.

[0106] S3. Preparation of flame-retardant reinforced linkage layer: 75 parts by weight of cross-linked polyethylene resin, 15 parts by weight of expanded graphite and 10 parts by weight of graphene are added to a high-speed mixer and mixed at 90°C for 12 minutes to obtain mixture B; mixture B is extruded at 170°C using an extruder, and grooves are simultaneously formed through a die at an extrusion speed of 15 m / min, and flame-retardant elastic elements are immediately filled after the grooves are formed.

[0107] The method for preparing the flame-retardant elastic component is as follows: 70 parts by weight of silicone rubber and 30 parts by weight of magnesium hydroxide powder are mixed, kneaded and molded, and then vulcanized at 130°C for 20 minutes to obtain the flame-retardant elastic component.

[0108] S4. Composite treatment: Align the thermally conductive and flame-retardant buffer layer with interlocking protrusions prepared in step S2 with the flame-retardant reinforced linkage layer with grooves and flame-retardant elastic elements prepared in step S3, and composite it through a hot pressing process at a composite temperature of 180°C, so that the interlocking protrusions are embedded in the grooves and in contact with the flame-retardant elastic elements.

[0109] The hot pressing process uses a pressure roller device with a matching convex and concave structure. The pressure roller temperature is 180℃ and the pressure is 2.0MPa.

[0110] S5. Crosslinking treatment: The composite structure is subjected to irradiation crosslinking with an irradiation dose of 15 MGry and an irradiation time of 40 minutes.

[0111] The irradiation crosslinking was carried out using an electron accelerator with an electron energy of 3 MeV.

[0112] S6. Preparation of outer sheath layer: Low smoke halogen-free flame retardant material is extruded at 190°C and coated on the cross-linked flame retardant and reinforced linkage layer. The extrusion speed is 22m / min. After cooling and shaping, the finished cable is obtained.

[0113] The low-smoke halogen-free flame retardant material is composed of the following components: 60 parts by weight of polyolefin, 30 parts by weight of aluminum hydroxide, 10 parts by weight of magnesium hydroxide and 5 parts by weight of lubricant.

[0114] The cooling and shaping process uses water cooling at a temperature of 30°C for 10 minutes.

[0115] Comparative Example 1

[0116] The difference between this comparative example and Example 1 is that the shape memory polymer component is removed from the material of the thermally conductive and flame-retardant buffer layer, while the remaining raw material ratios and preparation processes are the same as in Example 1.

[0117] Comparative Example 2

[0118] The difference between this comparative example and Example 1 is that boron nitride is replaced with an equal part by weight of calcium carbonate in the material of the thermally conductive and flame-retardant buffer layer, while the other raw material ratios and preparation processes are the same as in Example 1.

[0119] Comparative Example 3

[0120] The difference between this comparative example and Example 1 is that in the material of the flame-retardant reinforced linkage layer, expanded graphite is replaced with an equal part by weight of talc powder, while the other raw material ratios and preparation processes are the same as in Example 1.

[0121] Comparative Example 4

[0122] The difference between this comparative example and Example 1 is that in the preparation of the flame-retardant elastic component, the magnesium hydroxide wrapped in silicone rubber is replaced with an equal amount of calcium carbonate component, while the remaining raw material ratios and preparation processes are the same as in Example 1.

[0123] Comparative Example 5

[0124] The difference between this comparative example and Example 1 is that the material of the heat-conducting microtube embedded in step S2 is replaced by polyethylene plastic instead of copper. The inner diameter, wall thickness and internal heat-conducting medium of the microtube are the same as those in Example 1. The remaining raw material ratios and preparation processes are the same as those in Example 1.

[0125] Comparative Example 6

[0126] The difference between this comparative example and Example 1 is that in step S2, the thermally conductive microtubes are not embedded simultaneously during the extrusion process, but are drilled and embedded after the thermally conductive and flame-retardant buffer layer has been extruded, shaped and cooled. The remaining raw material ratios and preparation processes are the same as in Example 1.

[0127] Comparative Example 7

[0128] The difference between this comparative example and Example 1 is that: in step S4, the hot pressing process for compounding is omitted, and the two layers prepared in steps S2 and S3 are simply compounded together by a common co-extrusion die head, relying on the self-adhesive bonding of the molten material. The remaining raw material ratios and preparation processes are the same as in Example 1.

[0129] I. Test of the synergistic performance of flame retardancy and thermal conductivity under thermal stress

[0130] Experimental Procedure: Cable samples from Examples 1-3 and Comparative Examples 1-7 were selected. For each type of sample, a complete cable segment with a length of 500 mm was cut. The end 20 mm of the outer sheath was removed to expose the flame-retardant reinforcement interlocking layer. The sample was horizontally fixed on an experimental platform equipped with a temperature monitoring module and a vertical combustion test device. The thermocouple probes of the temperature monitoring module were attached to the conductor surface, the interface between the thermally conductive flame-retardant buffer layer and the flame-retardant reinforcement interlocking layer, and the outer surface of the flame-retardant reinforcement interlocking layer, respectively. The temperature measurement accuracy was controlled within ±0.5℃. The vertical combustion test device conformed to the GB / T18380.12-2008 standard.

[0131] A thermal stress scenario was simulated by applying 1.5 times the rated current to the conductor. Assuming the cable's rated current is 10A, a constant current of 15A was applied for 60 minutes, and the temperature change curves at each measuring point were recorded in real time. Immediately after 60 minutes of energization, the current was cut off. A flame was applied to the exposed area of ​​the flame-retardant reinforced linkage layer using a dedicated igniter according to GB / T18380.12-2008 standard, with the ignition time set to 12 seconds. The flame extinguishing time and whether any dripping material ignited the degreased cotton 100mm below were observed and recorded. At the same time, the maximum smoke density within 300 seconds of combustion was recorded using a smoke density tester conforming to GB / T17651.2-1998 standard.

[0132] After the experiment, the temperature rise was obtained by calculating the difference between the highest temperature and the initial temperature at each temperature measurement point under 60 minutes of thermal stress. The flame extinguishing time, ignition of the degreased cotton, and maximum smoke density of all samples were statistically analyzed and compared.

[0133] II. Cyclic Testing of Interlayer Bond Strength and Linkage Reliability

[0134] Experimental Procedure: Cable samples from Examples 1-3 and Comparative Examples 1-7 were selected. Three 200mm long cable segments were cut from each type of sample. The outer sheath and flame-retardant reinforcement layer were radially cut to form a 100mm long peel test sample between the thermally conductive and flame-retardant buffer layer and the flame-retardant reinforcement layer. A 50mm unpeeled segment was retained as the clamping end. A universal tensile testing machine with an accuracy of ±1N was used to perform interlayer peel strength testing according to GB / T2951.31-2008 standard. The tensile speed of the tensile testing machine was set to 50mm / min. The maximum peel force during the peeling process was recorded. The peel strength was calculated by dividing the maximum peel force by the sample width, where the sample width was taken as 1 / 4 of the cable circumference. After completing the initial peel strength test, three more 300mm long samples of the same type were taken for thermal stress cyclic linkage reliability testing. The samples were placed in a high-low temperature cycling chamber. The cycling conditions were set as follows: 80℃ for 2 hours, then naturally cooled to 25℃ for 1 hour. This constituted one cycle, and a total of 50 cycles were performed. After the cycle is completed, the sample is cut along the cable axis to observe the fit between the interlocking protrusions of the thermally conductive and flame-retardant buffer layer and the grooves of the flame-retardant reinforced linkage layer. Check for any protrusion detachment, groove deformation, or interlayer gaps. At the same time, the interlayer peel strength is retested according to the above peel strength test method, and the peel strength change rate is calculated. The calculation formula is:

[0135] .

[0136] The test data of flame retardant and thermal conductivity synergistic performance under thermal stress in Examples 1-3 and Comparative Examples 1-7 are shown in Table 1.

[0137] Table 1:

[0138]

[0139] Note:

[0140] 1. The temperature rise is the difference between "the highest temperature under 60 minutes of thermal stress and the initial temperature";

[0141] 2. The maximum smoke density is tested according to GB / T17651.2-1998. The lower the value, the better the flame retardant smoke exhaust performance.

[0142] Table 2 shows the interlayer bonding strength and linkage reliability cyclic test data of Examples 1-3 and Comparative Examples 1-7.

[0143] Table 2:

[0144]

[0145] Note:

[0146] 1. Peel strength is tested according to GB / T2951.31-2008; the higher the value, the stronger the interlayer bonding.

[0147] 2.50 cycles of linkage structure status classification criteria: "Excellent / Good / Poor"

[0148] Advantages: No protrusions fall off, no deformation in the grooves, and no gaps between layers;

[0149] Good: No protrusions fall off, no deformation in the grooves, and obvious interlayer gaps exist;

[0150] Poor: Some protrusions have fallen off, the edges of the grooves are cracked, and there are gaps between layers.

[0151] Based on the test data results of the above embodiments and comparative examples, the following conclusions are drawn:

[0152] 1. As can be seen from Examples 1-3 and Comparative Example 1 and Table 1, under thermal stress, the shape memory polymer can cause the interlocking protrusions to deform to squeeze the flame-retardant elastic element in the groove, thereby promoting the active release of flame retardant and adjusting the contact state of the thermally conductive microtube. If this component is removed, the dynamic linkage mechanism between the layers fails, and it is impossible to actively optimize the flame retardant and thermal conductivity performance under thermal stress, thus affecting the overall synergistic effect.

[0153] 2. Based on Examples 1-3 and Comparative Example 2, and in conjunction with Table 1, it can be seen that boron nitride mainly plays a directional heat conduction role in the thermally conductive and flame-retardant buffer layer. It can quickly transfer the heat generated by the conductor layer to the flame-retardant reinforcement layer to avoid local heat accumulation. If it is replaced with calcium carbonate, which has no obvious thermal conductivity, the heat conduction path of the buffer layer will be blocked, and the heat will be difficult to diffuse effectively. This will not only affect the heat conduction efficiency, but also indirectly weaken the flame-retardant performance due to excessively high local temperatures, thus destroying the synergistic relationship between flame retardancy and heat conduction.

[0154] 3. As can be seen from Examples 1-3 and Comparative Example 3 and Table 1, expanded graphite is the core component for achieving passive flame retardancy in the flame-retardant reinforced linkage layer. When heated, it can expand to form a dense heat-insulating carbon layer, which blocks the spread of flames and reduces heat transfer. If it is replaced with talc powder without expansion and heat insulation function, the linkage layer loses its key heat insulation barrier, the flame can penetrate into the interior more easily, and the heat will be transferred to the buffer layer more quickly, resulting in a significant decrease in flame retardant effect and failure to form an effective combination with thermal conductivity.

[0155] 4. Based on Examples 1-3 and Comparative Example 4, and in conjunction with Table 1, it can be seen that the magnesium hydroxide encapsulated in the flame-retardant elastic component is a flame-retardant substance that can be actively released under thermal stress. When the interlocking protrusions compress the elastic component, the magnesium hydroxide can be released through micropores to enhance the local flame-retardant effect. If it is replaced with calcium carbonate, which has no flame-retardant effect, even if the elastic component is deformed by compression, it cannot release effective flame-retardant components. During the combustion process, it is difficult to suppress the spread of flame, so the synergistic effect of flame-retardant performance and thermal conductivity cannot be realized.

[0156] 5. As can be seen from Examples 1-3 and Comparative Example 5 and Table 1, copper thermally conductive microtubes are the key structure for enhancing directional heat conduction in the thermally conductive and flame-retardant buffer layer. Copper has excellent thermal conductivity and can quickly transfer the heat of the conductor to the linkage layer. If it is replaced with polyethylene plastic microtubes with extremely low thermal conductivity, the efficiency of the heat conduction path will be greatly reduced, and heat will easily accumulate in the buffer layer. This will not only affect the overall thermal conductivity, but also increase the flame-retardant pressure due to the local temperature rise, weakening the synergistic effect of the two.

[0157] 6. As can be seen from Examples 1-3 and Comparative Example 6 and Table 2, synchronous embedding of thermally conductive microtubes during extrusion is an important process to ensure the structural integrity of the thermally conductive and flame-retardant buffer layer. Synchronous embedding can make the microtubes tightly bonded to the buffer layer matrix, avoiding damage to the protruding structure. If post-processing drilling is used for embedding, the drilling process is prone to causing cracking of the protrusions and blockage of micropores, which will damage the structural integrity of the interlayer and reduce the interlayer bonding strength, thus affecting the stability of the linkage structure in repeated use.

[0158] 7. As can be seen from Examples 1-3 and Comparative Example 7 and Table 2, the hot pressing composite process with matching convex and concave structures of the pressure roller can ensure that the interlocking protrusions of the thermally conductive and flame-retardant buffer layer and the grooves of the flame-retardant and reinforced linkage layer are precisely fitted, thereby enhancing the interlayer bonding force. If the hot pressing process is cancelled and ordinary co-extrusion is used instead, the interlayer bonding cannot be achieved by relying solely on the viscosity of the molten material itself, which easily forms interlayer gaps. This not only reduces the initial peel strength but also further aggravates the loosening of the structure during repeated use, affecting the reliability of the linkage structure.

[0159] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A multi-layered, flame-retardant, heat-conductive, cross-linked polyethylene cable construction, characterized by: From inside to outside, it includes conductor layer (1), heat-conducting and flame-retardant buffer layer (2), flame-retardant and enhanced linkage layer (3) and outer sheath layer (4); The conductor layer (1) is silver-plated copper conductor, and the thickness of the silver-plated layer is 0.05-0.1 mm; The heat-conducting and flame-retardant buffer layer (2) is made of materials containing 60-70 parts by weight of cross-linked polyethylene matrix, 15-20 parts by weight of boron nitride, 10-15 parts by weight of aluminum hydroxide and 5-8 parts by weight of shape memory polymer; the outer surface of the heat-conducting and flame-retardant buffer layer (2) is provided with interlocking protrusions (201), the interlocking protrusions (201) are internally embedded with heat-conducting microtubes (202), and the sidewalls of the interlocking protrusions (201) are provided with micropores (203); The flame-retardant and enhanced linkage layer (3) is made of materials containing 65-75 parts by weight of cross-linked polyethylene matrix, 10-15 parts by weight of expanded graphite and 5-10 parts by weight of graphene; the inner surface of the flame-retardant and enhanced linkage layer (3) is provided with grooves (301) matched with the shapes of the interlocking protrusions (201), and the grooves (301) are provided with flame-retardant elastic members (302); The flame-retardant elastic member (302) is a composite structure formed by wrapping silicon rubber around magnesium hydroxide, and the mass percentage content of magnesium hydroxide is 30%-40%.

2. A process for the preparation of a multi-layered flame-retardant heat-conductive cross-linked polyethylene cable structure, characterized in that, A multi-layer flame-retardant and heat-conducting cross-linked polyethylene cable structure for claim 1, comprising the following steps: S1, preparing a conductor layer: silver plating treatment is performed on copper material, the silver plating temperature is controlled at 50-60℃, the silver plating time is 30-40 minutes, and then a conductor with a required cross section is prepared through a drawing process; S2, preparing a heat-conducting and flame-retardant buffer layer: 60-70 parts by weight of cross-linked polyethylene resin, 15-20 parts by weight of boron nitride powder, 10-15 parts by weight of aluminum hydroxide powder and 5-8 parts by weight of shape memory polymer particles are added into a high-speed mixer, mixed at 80-100℃ for 5-15 minutes to obtain a mixture A; the mixture A is extruded into a shape at 120-160℃ by using an extruder, and a heat-conducting microtube (202) is embedded in the extruding process, a heat-conducting and flame-retardant buffer layer with interlocking protrusions (201) and micropores (203) is formed by molding through a mold, and the extrusion speed is 10-20 m / min; S3, preparing a flame-retardant and enhanced linkage layer: 65-75 parts by weight of cross-linked polyethylene resin, 10-15 parts by weight of expanded graphite and 5-10 parts by weight of graphene are added into a high-speed mixer, mixed at 70-90℃ for 8-12 minutes to obtain a mixture B; the mixture B is extruded at 130-170℃ by using an extruder, a groove (301) is simultaneously molded by using a mold, the extrusion speed is 8-15 m / min, and a flame-retardant elastic member (302) is filled into the groove (301) immediately after the molding of the groove (301); S4, composite processing: the heat-conducting and flame-retardant cushion layer with interlocking protrusions prepared in step S2 is aligned with the flame-retardant and reinforcing linkage layer with grooves and flame-retardant elastic members prepared in step S3, and then composite processing is performed by hot pressing at a temperature of 140-180℃, so that the interlocking protrusions (201) are embedded in the grooves (301) and contact the flame-retardant elastic members (302); S5, cross-linking processing: the composite structure is subjected to irradiation cross-linking at a dose of 5-15 MeV for 20-40 minutes; S6, preparation of an outer sheath layer: low-smoke and halogen-free flame-retardant material is extruded at 150-190℃ to coat the flame-retardant and reinforcing linkage layer after cross-linking, at an extrusion speed of 12-22 m / min, and then cooled and shaped to obtain a finished cable.

3. A process for the preparation of a multi-layered flame retardant heat conductive crosslinked polyethylene cable construction according to claim 2, characterized in that: In step S2, the heat-conducting microtubes (202) are made of copper, have an inner diameter of 0.5-1 mm and a wall thickness of 0.1-0.2 mm, and are of a closed structure filled with a heat-conducting medium.

4. A process for the preparation of a multi-layered flame retardant heat conductive crosslinked polyethylene cable construction as claimed in claim 2, wherein: In step S3, the flame-retardant elastic members (302) are prepared by mixing 60-70 parts by weight of silicone rubber with 30-40 parts by weight of magnesium hydroxide powder, mixing and molding, and then vulcanizing at a temperature of 110-130℃ for 10-20 minutes.

5. A process for the preparation of a multi-layered flame retardant heat conductive crosslinked polyethylene cable construction as claimed in claim 2, wherein: In step S4, the hot pressing process uses a roller device with matching convex and concave structures, at a temperature of 140-180℃ and a pressure of 0.5-2.0 MPa.

6. A process for the preparation of a multi-layered flame retardant heat conductive crosslinked polyethylene cable construction as claimed in claim 2, wherein: In step S5, the irradiation cross-linking is performed by an electron accelerator at an electron energy of 1-3 MeV.

7. The manufacturing process of a multilayer flame-retardant and thermally conductive cross-linked polyethylene cable structure according to claim 2, characterized in that: In step S6, the low-smoke and halogen-free flame-retardant material is composed of 50-60 parts by weight of polyolefin, 20-30 parts by weight of aluminum hydroxide, 5-10 parts by weight of magnesium hydroxide, and 3-5 parts by weight of a lubricant.

8. A process for the preparation of a multi-layered flame retardant heat conductive crosslinked polyethylene cable construction as claimed in claim 2, wherein: In step S6, the cooling and shaping is performed by water cooling at a temperature of 20-30℃ for 5-10 minutes.

Images