Flexible fireproof flame-retardant crosslinked polyethylene power cable

Abstract

The invention relates to the technical field of cable manufacturing, and discloses a flexible fireproof flame-retardant crosslinked polyethylene power cable, an insulating layer of which is prepared from the following raw materials: a component A, a component B, a component C and a component D, the composition comprises an ethylene-octylene copolymer, metallocene linear low density polyethylene, a maleic anhydride grafted styrene-ethylene-butylene-styrene block copolymer and an antioxidant, the component B comprises active magnesium hydroxide with an ionized coating layer formed on the surface, micro-powder grade magnesium hydroxide, zinc borate, zinc methacrylate and phenyl silicone rubber powder; and the component C is a crosslinking aid solution, and the crosslinking aid solution comprises vinyl trimethoxy silane, dicumyl peroxide, alpha-methyl styrene dimer and dibutyltin dilaurate. Zinc methacrylate is used for coating magnesium hydroxide and zinc borate in situ, an ionized flame-retardant filler system is constructed in cooperation with phenyl siloxane rubber, the interfacial compatibility is improved, and all the components react synergistically at a high temperature to generate a compact ceramic layer.

Description

Technical Field

[0001] This invention relates to the field of cable manufacturing technology, specifically to a flexible, fire-resistant, and flame-retardant cross-linked polyethylene power cable. Background Technology

[0002] With the rapid development of urban rail transit, shipbuilding, and high-rise buildings, power transmission systems face increasingly complex installation environments. Cables often need to be laid in narrow, winding channels, requiring insulation materials to possess excellent flexibility to withstand frequent bending and deformation. Simultaneously, to ensure public safety in extreme situations, these cables must possess superior fire-retardant properties, capable of slowing the spread of fire in the event of a fire and maintaining the electrical integrity of the circuit as much as possible to prevent secondary short circuits caused by insulation failure.

[0003] In existing technologies, low-density polyethylene or ethylene-vinyl acetate copolymer is typically selected as the matrix resin, combined with metal hydroxides such as aluminum hydroxide and magnesium hydroxide as flame retardants. Utilizing silane grafting and warm water crosslinking technology, a network structure can be formed between polymer molecular chains through hydrolysis and condensation reactions after molding. This technical approach significantly improves the material's heat resistance, mechanical strength, and chemical corrosion resistance, while producing low smoke emissions and no toxic or corrosive gases during combustion, meeting modern environmental protection requirements.

[0004] However, traditional inorganic flame retardants have limited efficiency and typically require extremely high filler volumes to meet fire resistance standards. This severely disrupts the continuous phase of the resin matrix, leading to a significant increase in material hardness and a sharp decrease in elongation at break, making it impossible to balance high flame retardancy with high flexibility. During manufacturing, the high-filler-volume powder generates intense friction with the screw and barrel, resulting in uncontrolled shear heat that causes a rapid rise in material temperature. This induces peroxide decomposition, causing premature local cross-linking of the silane cross-linking system within the extruder, resulting in rough cable surfaces and even dead glue. Furthermore, commonly used porous inorganic fillers readily physical adsorb liquid silane additives, hindering the diffusion and grafting of silane molecules onto the resin backbone. This competitive adsorption effect directly reduces grafting efficiency, often resulting in the final product's cross-linking degree failing to meet expectations. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a flexible fire-resistant and flame-retardant cross-linked polyethylene power cable, which solves the technical problems of significant decrease in mechanical flexibility of existing cross-linked polyethylene cable materials under high-filling flame-retardant systems, scorching caused by shear thermal runaway during silane grafting extrusion, and loose residues after combustion that cannot form a dense protective layer.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a flexible fire-resistant and flame-retardant cross-linked polyethylene power cable, employing the following technical solution: A flexible, fire-retardant, cross-linked polyethylene power cable includes a conductor and an insulation layer covering the conductor. The insulation layer is made from raw materials comprising the following parts by weight through reactive extrusion and hydrolytic cross-linking: Component A, a resin matrix mixture of 100 to 120 parts; Component B, an ionized modified flame-retardant filler composition of 130 to 150 parts; and Component C, a cross-linking aid liquid of 1.5 to 3.0 parts. Component A, the resin matrix mixture, comprises ethylene-octene copolymer, metallocene linear low-density polyethylene, maleic anhydride-grafted styrene-ethylene-butene-styrene block copolymer, and an antioxidant; Component B, the ionized modified flame-retardant filler composition, comprises active magnesium hydroxide with an ionized coating layer formed on its surface, micronized magnesium hydroxide, zinc borate, zinc methacrylate, and phenyl silicone rubber powder; and Component C, the cross-linking aid liquid, comprises vinyltrimethoxysilane, dicumyl peroxide, α-methylstyrene dimer, and dibutyltin dilaurate.

[0007] By adopting the above technical solution, and utilizing a resin matrix with a specific ratio of ionized modified filler and an anti-scorching crosslinking system, the synergistic effect of each component improves the material performance. The specific mechanism is as follows: First, zinc methacrylate was used to modify the surface of inorganic flame-retardant fillers. During processing, molten zinc methacrylate coated the surfaces of magnesium hydroxide and zinc borate. Its polar groups interacted with the surface of the inorganic fillers, and its long carbon chains were compatible with the resin matrix. This interfacial structure improved the dispersibility of inorganic powders in the resin matrix under high filler content, reduced melt viscosity, and maintained the material's flexibility and elongation at break. Simultaneously, zinc methacrylate participated in the crosslinking reaction, constructing ionic crosslinks in the matrix and improving the material's strength.

[0008] Secondly, a high-temperature self-crosslinking ceramic system with an organic-inorganic hybrid structure is constructed. When the cable is exposed to high temperatures, the following changes occur: Dehydration to carbonization: Magnesium hydroxide decomposes at 340℃ to 490℃ to release water of crystallization and form a magnesium oxide framework; zinc borate releases water of crystallization and melts to form a glassy substance.

[0009] In-situ ceramic formation: When the temperature is raised to above 600℃, the phenyl silicone rubber powder undergoes thermal oxidation and degradation to generate amorphous silica; zinc methacrylate undergoes thermal decomposition to generate zinc oxide micro powder.

[0010] Sintering and solidification: Zinc oxide, silicon dioxide, and magnesium oxide undergo a solid-state reaction under the action of zinc borate melt, forming a multi-element eutectic ceramic phase mainly composed of zinc silicate, magnesium silicate, and borosilicate. This ceramic layer is dense, isolating oxygen and heat, and preventing further combustion of the insulating layer.

[0011] Furthermore, α-methylstyrene dimer is introduced as a free radical regulator to suppress scorching during the grafting process. In reactive extrusion, the α-methylstyrene dimer captures macromolecular free radicals, inhibiting carbon-carbon bond coupling side reactions without affecting the grafting reaction of vinyltrimethoxysilane. This effect broadens the processing temperature window and ensures the flow stability of the material.

[0012] Preferably, the A component resin matrix mixture is composed of the following raw materials in parts by weight: 55 to 85 parts of ethylene-octene copolymer, 20 to 45 parts of metallocene linear low-density polyethylene, 5 to 15 parts of maleic anhydride-grafted styrene-ethylene-butene-styrene block copolymer, and 0.1 to 1.0 parts of antioxidant.

[0013] By adopting the above technical solution, ethylene-octene copolymer provides flexible segments, metallocene linear low-density polyethylene provides mechanical strength and heat resistance, and maleic anhydride-grafted styrene-ethylene-butene-styrene block copolymer serves as a compatibilizer. By utilizing the chemical bonding between the anhydride groups and the filler surface, the interfacial bonding force between the resin and the filler is enhanced, so that the material can maintain a high filling amount while having an elongation at break greater than 175%.

[0014] Preferably, the ionized modified flame retardant filler composition of component B is made from the following raw materials in parts by weight: 90 to 110 parts of active magnesium hydroxide, 15 to 25 parts of micronized magnesium hydroxide, 8 to 12 parts of zinc borate, 3 to 8 parts of zinc methacrylate, and 4 to 8 parts of phenyl silicone rubber powder.

[0015] By employing the above technical solution, magnesium hydroxide of different particle sizes is used for graded filling to improve the powder bulk density. Zinc methacrylate ensures the coating effect on the filler surface, phenyl silicone rubber powder provides the silicon source, and the phenyl groups improve the high-temperature thermal stability and char residue of the material, promoting the formation of the ceramic layer.

[0016] Preferably, the C component crosslinking aid liquid is composed of the following raw materials in parts by weight: 1.8 to 2.5 parts of vinyltrimethoxysilane, 0.1 to 0.2 parts of dicumyl peroxide, 0.05 to 0.12 parts of α-methylstyrene dimer, and 0.03 to 0.08 parts of dibutyltin dilaurate.

[0017] By employing the above technical solution and controlling the ratio of initiator to regulator, gel formation is suppressed. Dibutyltin dilaurate catalyzes the subsequent hydrolysis-condensation reaction, enabling the insulation layer to form a three-dimensional network cross-linked structure in a warm water environment, thereby improving the cable's resistance to environmental stress cracking and heat deformation.

[0018] Preferably, the octene comonomer in the ethylene-octene copolymer has a mass fraction of 25% to 35% and a density of 0.86 g / cm³ to 0.88 g / cm³; the styrene block content in the maleic anhydride-grafted styrene-ethylene-butene-styrene block copolymer is 20% to 30%, and the maleic anhydride grafting rate is 1.0% to 1.5%.

[0019] By adopting the above technical solution, ethylene-octene copolymer with high octene content and low density is selected to reduce the crystallinity of the system; the grafting rate of the compatibilizer is controlled to ensure the reactive sites, while avoiding the increase in water absorption due to excessive polarity.

[0020] Preferably, the ionized modified flame retardant filler composition of component B is prepared by the following method: active magnesium hydroxide, micronized magnesium hydroxide and zinc borate are mixed and heated to 105°C to 115°C for dehydration; then zinc methacrylate and phenyl silicone rubber powder are added, the temperature is raised to 120°C to 130°C and sheared and mixed to melt zinc methacrylate and form an ionized coating layer on the filler surface.

[0021] By employing the above technical solution, dehydration treatment removes physically adsorbed water from the surface of the filler, preventing it from affecting the coupling effect. Shearing at a temperature above the melting point of zinc methacrylate achieves uniform coating of the modifier, constructing a core-shell structure and preventing filler agglomeration.

[0022] Secondly, the present invention provides a method for preparing a flexible fire-resistant and flame-retardant cross-linked polyethylene power cable, which adopts the following technical solution: A method for preparing a flexible, fire-resistant, and flame-retardant cross-linked polyethylene power cable includes the following steps: Step 1: Prepare the A component resin matrix mixture, the C component crosslinking aid liquid homogeneous solution, and the pre-prepared B component ionized modified flame retardant filler composition according to the specified ratios. Step 2: Reaction granulation is carried out using a co-rotating parallel twin-screw extruder. Component A is added from the main feed port, component C is injected from the liquid injection port located in the screw conveying melting zone or grafting reaction zone, and component B is added from the side feed port located in the middle and rear section of the screw. The material is extruded, pelletized, and dried to obtain insulating material particles. Step 3: The insulating particles are extruded onto the conductor using a single-screw extruder, and then cross-linked in a warm water or steam environment.

[0023] By adopting the above technical solution, the present invention employs a segmented reactive extrusion process, the specific principle and effects of which are as follows: First, the chemical grafting and physical blending are carried out in stages. In the front section of the screw, component A resin is mixed with component C crosslinking aid liquid. In this area, there is no interference from inorganic fillers, and vinyltrimethoxysilane is efficiently grafted onto the polyethylene molecular backbone, improving the grafting rate.

[0024] Secondly, controlling the material temperature rise prevents scorching. Component B flame-retardant filler is added to the middle and rear section of the screw through a side feed port, at which point the grafting reaction is basically complete. This post-feeding method reduces the frictional heat generated by the filler particles in the high-shear zone, and together with α-methylstyrene dimer, prevents early cross-linking of the material within the extruder, ensuring extrusion stability.

[0025] Finally, a uniform interfacial structure is formed. When the resin matrix grafted with silane groups is mixed with the ionized modified component B filler, the interaction between polar groups promotes the dispersion of inorganic fillers, eliminates agglomeration, and maintains mechanical properties while ensuring the flame retardant rating.

[0026] Preferably, in step two, the temperature control of the co-rotating parallel twin-screw extruder is as follows: the conveying melting zone is 140°C to 155°C; the grafting reaction zone is 170°C to 185°C; the blending and dispersion zone is 155°C to 165°C; and the die head temperature is 145°C to 155°C.

[0027] By adopting the above technical solution, a temperature gradient is established. A higher temperature is set in the grafting reaction zone to provide activation energy and promote the grafting reaction; the temperature is lowered in the blending and dispersion zone to balance the shear heat generated after the addition of filler and prevent excessive temperature from causing decomposition of the modifier or side reactions.

[0028] Preferably, in step two, the length-to-diameter ratio of the co-rotating parallel twin-screw extruder is greater than or equal to 48, the liquid injection port is located at 2D to 8D of the screw, and the side feed port is located at 20D to 32D of the screw.

[0029] By adopting the above technical solution, the large aspect ratio provides sufficient reaction time. The liquid injection port is positioned forward to ensure the premixing and reaction length of the additives and resin; the side feed port is positioned in the center and rear to ensure the mixing and dispersion zone of the filler, while avoiding interference with the grafting reaction in the preceding stage.

[0030] Preferably, in step three, the extrusion temperature of the single-screw extruder is 135°C to 160°C, and the highest temperature of the die head does not exceed 160°C; after the insulating particles are extruded onto the conductor, they are soaked in a constant temperature water bath at 85°C to 95°C for 4 to 8 hours.

[0031] By adopting the above technical solution, a lower temperature is used in the cable extrusion stage to suppress the premature condensation of silane groups at the die orifice, thus avoiding the formation of pre-crosslinked particles. Constant-temperature water immersion treatment allows moisture to penetrate into the insulation layer, and under the action of a catalyst, the silane grafted segments hydrolyze and condense, forming a three-dimensional network crosslinked structure.

[0032] This invention provides a flexible, fire-resistant, and flame-retardant cross-linked polyethylene power cable. It has the following beneficial effects: 1. This invention utilizes zinc methacrylate to in-situ coat magnesium hydroxide and zinc borate, combined with phenyl silicone rubber to construct an ionized flame-retardant filler system. This system is uniformly dispersed in the resin matrix. The long-chain structure of zinc methacrylate improves interfacial compatibility, and at high temperatures, the components synergistically react to form a dense ceramic layer. Compared with the traditional technical solution that achieves flame retardancy solely through high-filling magnesium hydroxide, this invention effectively overcomes the problem of decreased material mechanical properties caused by inorganic filler agglomeration. While significantly improving the limiting oxygen index, it can still maintain an elongation at break of over 175%, achieving a balance between high flame retardancy and high flexibility.

[0033] 2. This invention introduces α-methylstyrene dimer as a free radical regulator in the crosslinking aid solution. This regulator can selectively capture active macromolecular free radicals generated by the decomposition of peroxides and inhibit the direct coupling side reaction of carbon-carbon bonds, but does not interfere with the grafting process of vinyltrimethoxysilane. Compared with the existing technology that simply relies on reducing the processing temperature or reducing the amount of initiator to control scorching, this solution broadens the processing temperature window of the material, avoids the pre-crosslinking phenomenon in the extrusion process, and ensures that the surface of the cable insulation layer is smooth and flat.

[0034] 3. This invention employs a distributed reaction extrusion process with resin as the main feeder, front-end injection of auxiliary liquid, and side feeding of inorganic filler in the middle and rear sections. The resin and silane undergo a grafting reaction first in a filler-free region, and then are blended with flame-retardant filler at low temperature. Compared with the existing preparation process that mixes all raw materials and then extrudes them in one step, this method eliminates the physical adsorption of liquid silane auxiliary by porous inorganic filler, significantly improves grafting efficiency and crosslinking density, and reduces the residence time and frictional heat of materials in the high-shear zone, further ensuring the stability of the production process. Attached Figure Description

[0035] Figure 1 The following is a monitoring graph of the processing rheological properties of the test examples of the present invention, wherein (a) shows the dynamic change of torque during the extrusion process, and (b) shows the melt flow rate of each group; Figure 2 This is a comparison chart of the ceramization performance of the test examples of this invention at medium temperature sintering; Figure 3 This is a diagram showing the relationship between the mechanical properties and cross-linked networks of the test examples of the present invention, wherein (a) focuses on showing the difference in elongation at break, and (b) shows the relationship between toughness and degree of cross-linking. Figure 4 This is a diagram showing the flame retardant efficiency and electrical insulation distribution of the test examples of this invention. Detailed Implementation

[0036] 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.

[0037] 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.

[0038] The ethylene-octene copolymer (POE) uses octene comonomers with a mass fraction of 25%-35%, a melt flow rate (190℃, 2.16kg) of 1.0-3.0g / 10min, and a density of 0.86-0.88g / cm³. 3 ethylene-1-octene random copolymer.

[0039] Metallocene linear low-density polyethylene (m-LLDPE) with a density of 0.915-0.925 g / cm³ is selected. 3 ethylene-1-hexene copolymer with a melt flow rate (190℃, 2.16kg) of 1.0-2.0g / 10min.

[0040] Maleic anhydride-grafted styrene-ethylene-butene-styrene block copolymer (SEBS-g-MAH) is a graft copolymer with a styrene block content of 20%-30%, a hydrogenation degree greater than 98%, and a maleic anhydride grafting rate of 1.0%-1.5%.

[0041] Activated magnesium hydroxide is selected from hexagonal plate-shaped crystals treated with vinylsilane, with a median particle size d50 of 1.2-1.8 μm and a specific surface area of ​​4-6 m². 2 / g, purity greater than 99%.

[0042] The micronized magnesium hydroxide is made from untreated magnesium hydroxide powder with a median particle size d50 of 4.0-6.0 μm and a purity greater than 99%.

[0043] Zinc dimethacrylate (ZDMA) is selected from zinc dimethacrylate micro powder with a zinc content of 22%-24% and a water content of less than 0.5%, with CAS number 13189-00-9.

[0044] The phenyl silicone rubber powder is selected from polymethylphenylsiloxane powder with a phenyl molar content of 5%-10%, a vinyl content of less than 0.2%, and an average particle size of 10-30μm.

[0045] The α-methylstyrene dimer (MSD) is made of 2,4-diphenyl-4-methyl-1-pentene with a purity greater than 98%, CAS number 6362-80-7.

[0046] In addition to the main raw materials mentioned above, the vinyltrimethoxysilane (VTMS), dicumyl peroxide (DCP), dibutyltin dilaurate (DBTDL), zinc borate (2ZnO·3B2O3·3.5H2O), antioxidant 1010, antioxidant 168 and lubricant EBS used in this embodiment are all commercially available industrial-grade common chemicals.

[0047] Preparation Example 1: This preparation example provides a method for preparing an ionization-modified flame-retardant filler composition (denoted as filler A), comprising the following steps: 100 parts by weight of active magnesium hydroxide, 20 parts by weight of micronized magnesium hydroxide, and 10 parts by weight of zinc borate were added to a high-speed mixer with a heating jacket. The stirring speed was set to 500 rpm, and the heating was turned on to raise the material temperature to 110°C. The temperature was maintained for 5 minutes to remove physically adsorbed water from the powder surface. Then, 4 parts by weight of zinc methacrylate powder and 5 parts by weight of phenyl silicone rubber powder were added to the mixer. The stirring speed was increased to 1800 rpm, and the material temperature was raised to 125°C using high-speed shear heat and auxiliary heating. At this temperature, high-speed mixing was maintained for 10 minutes to melt the zinc methacrylate and form an ionized coating layer on the filler surface. Finally, the material was discharged into a cold mixer to cool to below 40°C, discharged, and sealed in packaging to obtain filler A.

[0048] Preparation Example 2: This preparation example provides a method for preparing an ionized modified flame retardant filler composition (denoted as filler B), which differs from Preparation Example 1 only in the amount of zinc methacrylate used, and includes the following steps: 100 parts by weight of active magnesium hydroxide, 20 parts by weight of micronized magnesium hydroxide and 10 parts by weight of zinc borate were added to a high-speed mixer and heated to 110°C at 500 rpm for 5 minutes. Then, 6 parts by weight of zinc methacrylate powder and 5 parts by weight of phenyl silicone rubber powder were added, the speed was adjusted to 1800 rpm and the temperature was raised to 125°C, and the mixture was high-speed mixed for 10 minutes. Finally, the material was cooled and discharged to obtain filler B.

[0049] Preparation Example 3: This preparation example provides a method for preparing an ionized modified flame retardant filler composition (denoted as filler C), which differs from Preparation Example 1 only in the amount of zinc methacrylate used, and includes the following steps: 100 parts by weight of active magnesium hydroxide, 20 parts by weight of micronized magnesium hydroxide and 10 parts by weight of zinc borate were added to a high-speed mixer and heated to 110°C at 500 rpm for 5 minutes. Then, 3 parts by weight of zinc methacrylate powder and 5 parts by weight of phenyl silicone rubber powder were added, the speed was adjusted to 1800 rpm and the temperature was raised to 125°C, and the mixture was high-speed mixed for 10 minutes. Finally, the material was cooled and discharged to obtain filler C.

[0050] Preparation Example 4: This preparation example provides a method for preparing a non-ionized modified comparative filler composition (denoted as filler D), which differs from Preparation Example 1 in that stearic acid is used instead of zinc methacrylate, and includes the following steps: 100 parts by weight of active magnesium hydroxide, 20 parts by weight of micronized magnesium hydroxide and 10 parts by weight of zinc borate were added to a high-speed mixer and heated to 110°C at 500 rpm for 5 minutes. Then, 4 parts by weight of stearic acid powder and 5 parts by weight of phenyl silicone rubber powder were added, the speed was adjusted to 1800 rpm and the temperature was raised to 125°C, and the mixture was high-speed mixed for 10 minutes. Finally, the filler D was obtained by cooling and discharging.

[0051] Example 1: This embodiment provides a flexible fire-resistant and flame-retardant cross-linked polyethylene power cable insulation material and its preparation method, including the following steps: (1) Preparation of materials: Weigh 70 parts by weight of ethylene-octene copolymer, 30 parts by weight of metallocene linear low-density polyethylene, 10 parts by weight of maleic anhydride grafted styrene-ethylene-butene-styrene block copolymer, 0.15 parts by weight of antioxidant 1010 and 0.35 parts by weight of antioxidant 168, and mix them evenly to obtain component A. Weigh 2.0 parts by weight of vinyltrimethoxysilane, 0.14 parts by weight of dicumyl peroxide, 0.08 parts by weight of α-methylstyrene dimer and 0.05 parts by weight of dibutyltin dilaurate, and premix them evenly to obtain homogeneous liquid component C; 139 parts by weight of the ionized modified flame retardant filler composition (filler A) prepared in Preparation Example 1 were selected as component B.

[0052] (2) Reactive extrusion granulation: A parallel twin-screw extruder with a length-to-diameter ratio of 52:1 is used. Component A is added through the main feed port, component C is injected through the liquid injection port located at 4D, and component B is added through the side feed port located at 24D.

[0053] The extruder temperature process parameters are set as follows: Conveying the melting zone (0-12D): 140℃-150℃; Grafting reaction zone (12-24D): 170℃-175℃ (In this region, dicumyl peroxide initiates the grafting of vinyltrimethoxysilane onto the resin backbone, and α-methylstyrene dimer inhibits macromolecular free radical coupling). Blending and dispersion zone (24-48D): 155℃-160℃ (Component B is added in this zone, and mechanical shearing is used to disperse the filler with zinc methacrylate coating. The low temperature setting prevents excessive thermal polymerization of double bonds). Head temperature: 150℃.

[0054] The main machine speed is set to 350 rpm. After the material is extruded, air-cooled and hot-cut on the die surface, and dried, grafted flame-retardant insulating material particles are obtained.

[0055] (3) Cable formation and cross-linking: The above-mentioned insulating material particles are added to a single screw extruder and extruded onto the conductor at an extrusion temperature of 135℃-155℃ (the highest temperature of the die head does not exceed 155℃) to form an insulating layer; then the cable is placed in a 90℃ constant temperature water bath for 5 hours to complete cross-linking through hydrolysis and condensation, and the finished cable is obtained.

[0056] Example 2: This embodiment provides a flexible fire-resistant and flame-retardant cross-linked polyethylene power cable insulation material and its preparation method, including the following steps: (1) Preparation of materials: Weigh 60 parts by weight of ethylene-octene copolymer, 40 parts by weight of metallocene linear low-density polyethylene, 10 parts by weight of maleic anhydride grafted styrene-ethylene-butene-styrene block copolymer, 0.15 parts by weight of antioxidant 1010 and 0.35 parts by weight of antioxidant 168, and mix them evenly to obtain component A; The amount and type of component C and component B (filler A) are the same as in Example 1.

[0057] (2) Reactive extrusion granulation: The process steps and parameters are exactly the same as in Example 1.

[0058] (3) Cable formation and cross-linking: The process steps and parameters are exactly the same as in Example 1.

[0059] Example 3: This embodiment provides a flexible fire-resistant and flame-retardant cross-linked polyethylene power cable insulation material and its preparation method, including the following steps: (1) Preparation of materials: The ratio of component A to component C is the same as in Example 1; 141 parts by weight of the ionized modified flame retardant filler composition (filler B) prepared in Preparation Example 2 were selected as component B.

[0060] (2) Reactive extrusion granulation: The process steps and parameters are exactly the same as in Example 1.

[0061] (3) Cable formation and cross-linking: The process steps and parameters are exactly the same as in Example 1.

[0062] Example 4: This embodiment provides a flexible fire-resistant and flame-retardant cross-linked polyethylene power cable insulation material and its preparation method, including the following steps: (1) Preparation of materials: The ratio of component A to component C is the same as in Example 1; 138 parts by weight of the ionized modified flame retardant filler composition (filler C) prepared in Preparation Example 3 were selected as component B.

[0063] (2) Reactive extrusion granulation: The process steps and parameters are exactly the same as in Example 1.

[0064] (3) Cable formation and cross-linking: The process steps and parameters are exactly the same as in Example 1.

[0065] Example 5: This embodiment provides a flexible fire-resistant and flame-retardant cross-linked polyethylene power cable insulation material and its preparation method, including the following steps: (1) Preparation of materials: The types and amounts of each component are completely consistent with those in Example 1.

[0066] (2) Reactive extrusion granulation: The temperature of the grafting reaction zone (12-24D) of the extruder was set to 180℃-185℃, while the temperature of the other zones and the main engine speed remained the same as in Example 1. At this higher temperature, the melt stability was maintained by the regulating effect of the α-methylstyrene dimer.

[0067] (3) Cable formation and cross-linking: The process steps and parameters are exactly the same as in Example 1.

[0068] Comparative Example 1: Compared with Example 1, the difference is that the non-ionic modified filler D prepared in Preparation Example 4 was selected in component B (using an equal mass of stearic acid to replace zinc methacrylate), and the proportions of the remaining raw materials and the preparation process are the same.

[0069] Comparative Example 2: Compared with Example 1, the difference is that the feeding method is changed. Component B (filler A), component A (resin matrix) and component C (liquid phase additive) are premixed evenly in a high-speed mixer and then added through the main feed port (OD). Side feeding is cancelled. The proportions of other raw materials and temperature parameters are the same.

[0070] Comparative Example 3: Compared with Example 1, the difference is that component C does not contain α-methylstyrene dimer (MSD), while the proportions of the remaining raw materials and the preparation process are the same.

[0071] Comparative Example 4: Compared with Example 1, the difference is that, using the same resin / filler ratio as in Example 1, only active magnesium hydroxide, micronized magnesium hydroxide and zinc methacrylate are added, while zinc borate and phenyl silicone rubber powder are removed, and the remaining raw material ratios and preparation processes are the same.

[0072] Comparative Example 5: Compared with Example 1, the difference is that component A does not contain SEBS-g-MAH, and the corresponding reduction in the number of parts is made up by ethylene-octene copolymer (POE). The proportions of other raw materials and the preparation process are the same.

[0073] Test Example 1: Test objective: To verify the effectiveness of the process kinetic control strategy of "side feeding and anti-scorching agent synergy" in this invention in preventing pre-crosslinking during the extrusion process while preserving the activity of functional monomers.

[0074] Experimental steps: 1. Online monitoring of extrusion torque: During the granulation production process of Examples 1 to 5 and Comparative Examples 2 to 3, after the twin-screw extruder entered a stable operating state of material conveying and plasticizing balance, the percentage value of the main extruder torque corresponding to the main extruder current load was continuously recorded. The recording time was set to 30 minutes, and the arithmetic mean within this time period was taken as the process torque data. If a sudden increase in torque exceeding 95% occurs during debugging or operation, causing the main extruder to shut down due to overload protection, this set of data is recorded as torque over-limit or shutdown.

[0075] 2. Melt Flow Rate Determination: Dry insulating material particles were randomly selected from the granulated products of each group mentioned above and tested according to the national standard GB / T 3682.1-2018 "Determination of Melt Mass Flow Rate (MFR) and Melt Volumetric Flow Rate (MVR) of Thermoplastic Plastics - Part 1: Standard Method". The test temperature was set at 190℃, the nominal load was 2.16 kg, and the cutting time interval was set at 10 seconds. Each sample was tested 5 times, and the arithmetic mean was taken. If the material strip could not flow out of the die or the surface of the extruded material was extremely rough and could not be effectively cut, it was determined that the test could not be conducted or that the material did not flow.

[0076] 3. Macroscopic quality assessment of particles: Spread the extruded and granulated sample evenly on a white enamel dish and visually inspect it under a standard light source. Pay particular attention to whether there are sharkskin-like patterns on the particle surface caused by melt fracture, and whether there are any visible gel lumps due to localized pre-crosslinking. The evaluation criteria are divided into three levels: Level A represents a bright, smooth particle surface with a dense cross-section; Level B represents a slightly rough surface or a matte finish but without obvious lumps; Level C represents a rough surface with obvious protruding particles or lumps.

[0077] The experimental data are shown in Table 1: Table 1: Processing rheology and surface quality test results of each embodiment and comparative example

[0078] Results analysis: Table 1 and Figure 1 The test data show that the process control strategy proposed in this invention has a significant impact on the processability of materials.

[0079] Comparative Example 2 employed a full-component main-feed process, resulting in the coexistence of zinc methacrylate and dicumyl peroxide in the high-temperature zone of the front section of the twin-screw extruder. Due to the highly reactive carbon-carbon double bonds of zinc methacrylate, under the initiation of dicumyl peroxide, zinc methacrylate and the polymer matrix underwent a vigorous free radical polymerization reaction in the molten state, forming a three-dimensional network structure. Data showed that the main extruder torque instantaneously overloaded, causing the equipment to shut down, and the mass flow rate of the forcibly removed melt was close to zero, indicating that the material had already experienced severe scorching during the granulation stage and lost its thermoplastic processing capability. This result confirms the necessity of a side-feed process that spatially isolates the active monomer zinc methacrylate from the initiator.

[0080] Comparative Example 3, although employing a side-feeding process, did not add α-methylstyrene dimer. Data showed its melt flow rate was only 0.32 g / 10 min, and numerous gel lumps existed on the particle surface. This indicates that in the grafting reaction zone, the free radicals of the polyethylene macromolecules were not effectively regulated, resulting in significant carbon-carbon coupling side reactions. The residual long-lived free radicals migrated to the blending zone and initiated localized polymerization of zinc methacrylate.

[0081] In Examples 1 to 5, the main motor torque remained stable between 61% and 69%, the melt flow rate remained between 1.4 and 2.0 g / 10 min, and the particle surface was smooth. This indicates that the competitive capture of free radicals by the α-methylstyrene dimer suppressed the side reactions in the grafting stage. Combined with the side-feeding technology, which moved the introduction point of zinc methacrylate to a relatively low temperature region, premature cross-linking of zinc methacrylate within the extruder was avoided while preserving the double bond activity. In Example 5, although the melt flow rate decreased slightly after increasing the grafting zone temperature to 185°C, it remained within the processable range, demonstrating that the process system has a wide operating window.

[0082] Test Example 2: Test objective: To verify the feasibility of the mechanism by which the zinc methacrylate in-situ catalytic system achieves rapid ceramization at medium temperature (600℃) and forms a high-strength protective shell under conditions without low-melting-point glass powder.

[0083] Experimental steps: 1. Pretreatment before high-temperature sintering: The cable insulation materials cross-linked with warm water prepared in Examples 1 to 5, as well as Comparative Examples 1, 4, and 5, were prepared into cuboid strips with dimensions of 50 mm in length, 10 mm in width, and 4 mm in thickness. The strips were placed horizontally in a clean alumina ceramic boat and then placed in the center of the isothermal zone of an SX2-4-10 type high-temperature muffle furnace.

[0084] 2. Medium-temperature simulated calcination program: Start the muffle furnace heating program, raising the furnace temperature from room temperature to 600℃ at a rate of 10℃ per minute, and maintain this temperature for 30 minutes to simulate the thermal environment during the middle stage of a fire. After the program ends, allow it to cool naturally to room temperature, carefully remove the porcelain boat, and visually observe the morphology of the sintered residue, recording whether it retains its original shape, whether there is severe shrinkage, cracking, or complete pulverization into ash.

[0085] 3. Ceramicized Shell Compressive Strength Test: The sintered residue sample was transferred to the compression fixture platform of the CMT-4000 universal testing machine. The compression rate was set to 2 mm / min, and pressure was applied vertically to the sample until it broke or collapsed. The system automatically recorded the maximum load force the sample experienced at the moment of breakage, in Newtons (N). For powdery or non-formable residues, the force value was recorded as 0 or a minimum value close to 0. Five parallel samples were tested in each group, and the arithmetic mean was taken.

[0086] The experimental data are shown in Table 2: Table 2: Test results of medium-temperature sintering ceramicization performance of each embodiment and comparative example

[0087] Results Analysis: Based on Table 2 and Figure 2 Data analysis shows that the low-temperature ceramicization system constructed in this invention exhibits significant ceramicization ability in a medium-temperature environment of 600℃.

[0088] Comparative Example 1 used stearic acid instead of zinc methacrylate, and its sintered product was a loose powder with a compressive strength of 0 N. This indicates that in the absence of active zinc oxide produced by the decomposition of zinc methacrylate as a flux, magnesium oxide produced by the decomposition of magnesium hydroxide cannot undergo a eutectic reaction with zinc borate and silicone rubber at 600°C; they only physically mix and cannot form a continuous ceramic skeleton.

[0089] Comparative Example 4 retained zinc methacrylate but removed zinc borate and phenyl silicone rubber powder, and its sintered product also lacked strength. This confirms that zinc methacrylate and magnesium hydroxide alone cannot form ceramics independently; a boron source and a silicon source are necessary to construct a zinc oxide-boron oxide-silica ternary eutectic system.

[0090] The samples from Examples 1 to 5 maintained their complete elongated geometric shape after sintering at 600℃ and possessed compressive strengths ranging from 10N to 18N, enabling them to withstand certain mechanical forces without breaking. In particular, Example 3, due to its higher zinc methacrylate content, exhibited an increased concentration of in-situ generated active zinc oxide, further promoting the formation of the glassy phase and the liquid-phase sintering between filler particles, thus demonstrating the highest shell strength (18.2N). This result confirms the in-situ catalytic mechanism proposed in this invention: the nano-active zinc oxide generated by the thermal decomposition of zinc methacrylate effectively reduces the activation energy and eutectic temperature of the ceramicization reaction, allowing the material to form a hard protective shell in the early, mid-temperature stage of a fire, thereby blocking further erosion by flames and oxygen and ensuring the integrity of the circuit during a fire.

[0091] Test Example 3: Test objective: To demonstrate the significant effect of ion cluster-mediated micro-interface slip mechanism on the elongation at break of materials and the stability of silane cross-linked networks under high-temperature loads.

[0092] Experimental steps: 1. Room Temperature Tensile Properties Test: The insulating material particles prepared in each example and comparative example were extruded using a single screw extruder to form specimens with a thickness of 1.0 mm. These specimens were then immersed in a 90℃ constant temperature water bath for 5 hours to complete cross-linking, and subsequently cut into 5A dumbbell-shaped specimens as specified in GB / T 1040.2 "Determination of Tensile Properties of Plastics Part 2: Test Conditions for Molded and Extruded Plastics". The specimens were placed on an electronic tensile testing machine, with the tensile speed set to 250 mm / min and the ambient temperature at 23±2℃. The maximum load and gauge length elongation at tensile fracture were recorded, and the tensile strength (MPa) and elongation at break (%) were calculated. Five specimens were tested in each group, and the arithmetic mean was taken after discarding invalid data that broke outside the gauge length.

[0093] 2. Thermal Elongation and High-Temperature Creep Test: A thermal elongation test is conducted according to GB / T 2951.21-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 21: Test Methods for Elastomer Compounds - Ozone Resistance Test - Thermal Elongation Test - Mineral Oil Immersion Test" to verify the degree of crosslinking of the material. The crosslinked dumbbell-shaped sample is taken and a load is suspended within the gauge length, generating a stress of 20 N / cm². The loaded sample is placed in an oven preheated to 200°C and maintained at that temperature for 15 minutes. The distance between the gauge lengths is measured, and the elongation under load is calculated. If the sample breaks in the oven, it is recorded as "Break / Unqualified".

[0094] The experimental data are shown in Table 3: Table 3: Mechanical properties and thermal elongation test results of each embodiment and comparative example

[0095] Results Analysis: Based on Table 3 and... Figure 3 Data analysis shows that the introduction of zinc methacrylate and the corresponding matrix design have a decisive impact on the mechanical behavior of the material.

[0096] Comparing the elongation at break of 215.6% in Example 1 with that of Comparative Example 1 (115.3%), both used the same amount of modifier, but their properties were drastically different. The stearic acid used in Comparative Example 1 only provided physical isolation and lubrication through its alkyl chain, resulting in weak interfacial bonding and an inability to effectively transfer stress under high filler conditions, leading to brittle fracture. In contrast, Example 1 utilized zinc methacrylate to construct an "ionic cluster interface," with its zinc ion ends anchored to the filler surface and double bond ends integrated into the polymer network. During stretching, the ionic bonds underwent reversible dissociation and recombination, consuming a significant amount of deformation energy, thereby significantly improving the elongation at break.

[0097] Compared to the 162.7% elongation at break of Example 1 and Comparative Example 5, the removal of the maleic anhydride-grafted styrene-ethylene-butene-styrene block copolymer resulted in a significant decrease in elongation at break. This indicates that the rubber-elastic styrene block copolymer provides an amorphous microenvironment with ionic clusters, promoting the grafting and dispersion of zinc methacrylate, and the two have a synergistic toughening effect.

[0098] Regarding thermal elongation data, the elongation at 200°C load in all embodiments was controlled between 55% and 75%, far below the standard requirement of 175%. This demonstrates that although zinc methacrylate, which may consume free radicals, and α-methylstyrene dimer, which hinders crosslinking, were introduced into the system, the main crosslinking network of vinyltrimethoxysilane remained intact under the formulation ratio of this invention, and the material possessed satisfactory high-temperature creep resistance. Example 3 showed a slight increase in elongation at load of 72% with high zinc methacrylate content, indicating that the excess monomeric double bonds had a slight competitive inhibition on silane grafting efficiency, but remained within a safe range.

[0099] Test Example 4: Test objective: To confirm that the introduction of ionized modification components maintains excellent flame retardancy without compromising the material's macroscopic electrical insulation properties due to the presence of metal ions.

[0100] Experimental steps: 1. Limiting Oxygen Index (LOI) Determination: The granules prepared in each group were molded into standard specimens with dimensions of 80mm × 10mm × 4mm. According to GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test", the specimens were vertically fixed inside a combustion chamber. The oxygen and nitrogen mixing flow rate ratio was adjusted, and the top of the specimen was ignited using an igniter. The combustion behavior and flame propagation of the specimen were observed. The minimum oxygen concentration at which the specimen could sustain combustion for just 3 minutes or reach a combustion length of 50mm was determined using the "lifting method". This value is the limiting oxygen index.

[0101] 2. Vertical Flammability Rating (UL-94) Assessment: Prepare specimens measuring 125mm × 13mm × 3.2mm and conduct vertical flammability tests according to the UL-94 standard. Fix the specimen vertically and place a receiving tray lined with medical cotton at a height of 300mm below. Apply a standard flame to the bottom of the specimen for 10 seconds, remove it, and record the flaming time t1. After the flame extinguishes, apply the flame again for 10 seconds and record the flaming time t2 and the flaming time t3. Observe whether burning droplets ignite the cotton. Based on the flaming time and the ignition of the droplets, rate the material as V-0, V-1, V-2, or no rating (NC). Five specimens are tested per group.

[0102] 3. Volume Resistivity Test: The granules are molded into square sheets with a thickness of 1 mm and a side length of 100 mm, and conditioned for 24 hours at 20℃ and 65% relative humidity. According to GB / T 1410-2006 "Test Methods for Volume Resistivity and Surface Resistivity of Solid Insulating Materials", a high-resistivity meter connected to a three-electrode system is used for testing. A DC voltage of 500 V is applied, and after charging for 1 minute, the leakage current or direct resistance value is read, and the volume resistivity (Ω·cm) is calculated. Three parallel samples are tested in each group, and the geometric mean is taken.

[0103] The experimental data are shown in Table 4: Table 4: Flame retardant and electrical performance test results of each embodiment and comparative example

[0104] Results Analysis: Based on Table 4 and... Figure 4 Data analysis shows that, after introducing ionized modification components, this invention successfully maintained the material's high flame retardancy and excellent electrical insulation.

[0105] Regarding flame retardant performance, the limiting oxygen index (LOI) of all embodiments remained above 35.8%, and the UL-94 V-0 rating was achieved, with the maximum afterflame time controlled within 3.1 seconds. This result indicates that although zinc methacrylate itself contains organic carbon chains, its decomposition product, zinc oxide, forms an effective solid-phase synergistic effect with zinc borate and phenyl silicone rubber in the system. In contrast, Comparative Example 1 (stearic acid modified, LOI 34.2%, V-1 rating) shows that the system using stearic acid easily decomposes during combustion to produce low-viscosity melt, causing molten droplets to ignite the defatted cotton, thus reducing the flame retardant rating. This conversely demonstrates that the zinc oxide generated in situ from zinc methacrylate in this invention promotes the densification of the char layer and inhibits the generation of molten droplets.

[0106] Regarding electrical insulation performance, the volume resistivity of Examples 1 to 5 remained at 10. 15 The order of magnitude is Ω·cm, far exceeding the 1×10⁻⁶ typically required for power cable insulation. 14 Ω·cm baseline. Although Example 3 introduced more zinc ions due to the increased amount of zinc methacrylate, resulting in a volume resistivity increase from 4.8 × 10⁻⁶ Ω·cm, the volume resistivity decreased from 4.8 × 10⁻⁶ Ω·cm. 15 Reduced to 1.5×10 15 The voltage reached Ω·cm, but no order-of-magnitude jump occurred. This confirms the microstructure control mechanism of the present invention: the introduction of metal ions (Zn... 2+ The ions are not free ions in the matrix, but are tightly bound by chemical bonds within the interface layer (ion cluster) between the inorganic filler and the resin matrix. This chemical anchoring effect limits the long-range migration ability of the ions, thus preventing the formation of leakage channels on a macroscopic scale and ensuring the insulation reliability of the material under high-voltage environments.

[0107] 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 flexible fire-resistant and flame-retardant cross-linked polyethylene power cable, characterized in that, It includes a conductor and an insulating layer covering the outside of the conductor, the insulating layer being made from raw materials comprising, by reactive extrusion and hydrolytic crosslinking: Component A resin matrix mixture: 100-120 parts by weight; Component B ionized modified flame retardant filler composition: 130-150 parts by weight; Component C crosslinking aid solution: 1.5-3.0 parts by weight; The A component resin matrix mixture comprises ethylene-octene copolymer, metallocene linear low-density polyethylene, maleic anhydride-grafted styrene-ethylene-butene-styrene block copolymer and antioxidant. The B-component ionized modified flame retardant filler composition comprises active magnesium hydroxide with an ionized coating layer formed on its surface, micronized magnesium hydroxide, zinc borate, zinc methacrylate, and phenyl silicone rubber powder. The C-component crosslinking aid liquid contains vinyltrimethoxysilane, dicumyl peroxide, α-methylstyrene dimer, and dibutyltin dilaurate.

2. The flexible fire-resistant and flame-retardant cross-linked polyethylene power cable according to claim 1, characterized in that, The A component resin matrix mixture is composed of the following raw materials in parts by weight: Ethylene-octene copolymer: 55-85 parts; Metallocene linear low-density polyethylene: 20-45 parts; Maleic anhydride-grafted styrene-ethylene-butene-styrene block copolymer: 5-15 parts; Antioxidant: 0.1-1.0 parts.

3. The flexible fire-resistant and flame-retardant cross-linked polyethylene power cable according to claim 1, characterized in that, The ionized modified flame retardant filler composition of component B is made from the following raw materials in parts by weight: Activated magnesium hydroxide: 90-110 parts; Micronized magnesium hydroxide: 15-25 parts; Zinc borate: 8-12 parts; Zinc methacrylate: 3-8 parts; Phenyl silicone rubber powder: 4-8 parts.

4. The flexible fire-resistant and flame-retardant cross-linked polyethylene power cable according to claim 1, characterized in that, The C-component crosslinking aid solution is composed of the following raw materials in parts by weight: Vinyltrimethoxysilane: 1.8-2.5 parts; Dicumyl peroxide: 0.1-0.2 parts; α-Methylstyrene dimer: 0.05-0.12 parts; Dibutyltin dilaurate: 0.03-0.08 parts.

5. The flexible fire-resistant and flame-retardant cross-linked polyethylene power cable according to claim 2, characterized in that, The ethylene-octene copolymer has a mass fraction of 25%-35% for octene comonomer and a density of 0.86-0.88 g / cm³. 3 The styrene block content in the maleic anhydride-grafted styrene-ethylene-butene-styrene block copolymer is 20%-30%, and the maleic anhydride grafting rate is 1.0%-1.5%.

6. The flexible fire-resistant and flame-retardant cross-linked polyethylene power cable according to claim 3, characterized in that, The ionized modified flame-retardant filler composition of component B is prepared by the following method: Active magnesium hydroxide, micronized magnesium hydroxide, and zinc borate are mixed and heated to 105°C-115°C for dehydration; then zinc methacrylate and phenyl silicone rubber powder are added, the temperature is raised to 120°C-130°C, and shear mixing is performed to melt zinc methacrylate and form the ionized coating layer on the filler surface.

7. A method for preparing a flexible fire-resistant and flame-retardant cross-linked polyethylene power cable according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Prepare a resin matrix mixture of component A, a homogeneous solution of crosslinking aid liquid of component C, and a pre-prepared flame retardant filler composition of component B according to the specified proportions. (2) Reaction granulation is carried out using a co-rotating parallel twin-screw extruder. Component A is added from the main feed port, component C is injected from the liquid injection port located in the screw conveying melting zone or grafting reaction zone, and component B is added from the side feed port located in the middle and rear section of the screw. The material is extruded, pelletized, and dried to obtain insulating material particles. (3) The insulating material particles are extruded onto the conductor using a single screw extruder, and then cross-linked in a warm water or steam environment.

8. The method for preparing the flexible fire-resistant and flame-retardant cross-linked polyethylene power cable according to claim 7, characterized in that, In step (2), the temperature control of the co-rotating parallel twin-screw extruder is as follows: Melting zone: 140℃-155℃; Grafting reaction zone: 170℃-185℃; Blending and dispersion zone: 155℃-165℃; Head temperature: 145℃-155℃.

9. The method for preparing the flexible fire-resistant and flame-retardant cross-linked polyethylene power cable according to claim 8, characterized in that, In step (2), the length-to-diameter ratio L / D of the co-rotating parallel twin-screw extruder is ≥48, the liquid injection port is located at 2D-8D of the screw, and the side feed port is located at 20D-32D of the screw.

10. The method for preparing the flexible fire-resistant and flame-retardant cross-linked polyethylene power cable according to claim 7, characterized in that, In step (3), the extrusion temperature of the single screw extruder is 135℃-160℃, and the highest temperature of the die head does not exceed 160℃; after the insulating material particles are extruded onto the conductor, they are soaked in a constant temperature water bath of 85℃-95℃ for 4-8 hours.

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