Flame-retardant wire insulating material for wiring of power distribution cabinet and preparation method of flame-retardant wire insulating material

Abstract

The invention relates to the technical field of flame-retardant material preparation. The invention discloses a flame-retardant electric wire insulating material for wiring of a power distribution cabinet and a preparation method of the flame-retardant electric wire insulating material. The flame-retardant modified polybutylene terephthalate composite material is prepared from the following components in parts by weight: 40-55 parts of modified polybutylene terephthalate matrix resin, 8-12 parts of a phosphorus-nitrogen-silicon-containing ternary synergistic flame retardant, 6-10 parts of an epoxy functionalized ethylene-methyl acrylate copolymer, 4-7 parts of sulfonated polyethersulfone microspheres, 10-15 parts of a nano magnesium hydroxide / aluminum oxide composite filler and 1-3 parts of an anti-corona agent. The component A comprises the following components in parts by weight: 0.5-1.2 parts of a heat stabilizer, 0.3-0.8 part of a lubricating agent, 0.6-1.0 part of a silane coupling agent and 0.5-1.5 parts of a polyhydric alcohol charring accelerant; wherein the modified polybutylene terephthalate matrix resin is copolyester which is terminated by a terminal hydroxyl group and is introduced with a flexible aliphatic chain segment, and the melt flow rate is 8-15g / 10min. The material provided by the invention is flame-retardant, safe and environment-friendly, reaches UL94V-0 level, has a limit oxygen index of 35%-39%, a bunched combustion smoke density of 32%-38% and a halogen acid gas release amount of 3.5-4.8 mg / g, and can control fire and reduce harm in a fire disaster.

Description

Technical Field

[0001] This invention relates to the field of flame retardant material preparation technology, and in particular to a flame retardant wire insulation material and preparation method for electrical distribution cabinet wiring. Background Technology

[0002] As a power distribution unit in a power system, the internal wiring of a distribution cabinet must operate in a complex environment characterized by high temperature, high voltage, and dense components for extended periods. Therefore, stringent requirements are placed on the comprehensive performance of the wire insulation materials. These materials must not only possess stable electrical insulation capabilities but also achieve highly efficient flame retardancy under fire risks, while simultaneously preventing the release of harmful substances to ensure the safety of the power distribution system and personnel evacuation. However, traditional distribution cabinet wire insulation materials struggle to meet these multi-dimensional performance requirements. While some materials achieve flame retardancy through halogen-containing components, they produce large amounts of toxic gases and corrosive substances during combustion, endangering human health and potentially causing secondary damage to the precision components inside the cabinet. This fails to meet the environmental and safety standards of modern power equipment.

[0003] While existing halogen-free flame-retardant insulation materials have made breakthroughs in environmental protection, they often fall into the dilemma of incompatibility between flame retardancy and other properties. To improve flame retardancy, most materials require the addition of large amounts of inorganic flame-retardant fillers. These fillers are prone to compatibility issues with the polymer matrix, leading to a decrease in insulation resistance and unstable dielectric properties. Over long-term use, these materials are susceptible to cracking and peeling due to aging. Simultaneously, some halogen-free materials lack sufficient corona resistance and aging resistance. Under high voltage stress, conductive carbonization marks easily form on the material surface, causing leakage faults and failing to meet the reliability requirements for long-term stable operation of distribution cabinets.

[0004] Furthermore, the industrial application of high-performance insulation materials is currently limited by manufacturing processes. Some formulations, in order to balance multiple properties, require special reaction equipment or complex processing procedures, which not only increases production costs but also reduces production efficiency. Other materials, due to poor melt flowability and insufficient molding stability, are prone to uneven insulation layer thickness and surface defects during wire wrapping, affecting the consistency of finished product quality. These technological bottlenecks make it difficult for existing materials to fully meet the actual needs of wiring inside distribution cabinets. Developing an insulation material that balances high safety, high reliability, and high processability has become an urgent need for the industry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention discloses a flame-retardant wire insulation material and its preparation method for distribution cabinet wiring. This material possesses high volume resistivity, excellent aging resistance, and anti-corona capability, is suitable for the internal wiring requirements of distribution cabinets with rated voltages of 0.6 / 1kV and below, and can ensure the safe and stable operation of the power distribution system under complex working conditions of high temperature and high voltage.

[0006] This invention discloses a flame-retardant wire insulation material for wiring in distribution cabinets, which is made of the following components in parts by weight:

[0007] The composition includes: 40-55 parts modified polybutylene terephthalate matrix resin, 8-12 parts phosphorus-nitrogen-silicon ternary synergistic flame retardant, 6-10 parts epoxy-functionalized ethylene-methyl acrylate copolymer, 4-7 parts sulfonated polyethersulfone microspheres, 10-15 parts nano magnesium hydroxide / alumina composite filler, 1-3 parts anti-corona agent, 0.5-1.2 parts heat stabilizer, 0.3-0.8 parts lubricant, 0.6-1.0 parts silane coupling agent, and 0.5-1.5 parts polyol char formation accelerator.

[0008] Among them, the modified polybutylene terephthalate matrix resin is a copolyester with hydroxyl-terminated end-capped and flexible aliphatic segments introduced, and the melt flow rate is 8-15 g / 10 min.

[0009] Furthermore, the phosphorus-nitrogen-silicon ternary synergistic flame retardant is a cage-type silsesquioxane derivative grafted with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, with a phosphorus content ≥8wt% and a silicon content ≥12wt%.

[0010] Furthermore, the epoxy equivalent in the epoxy-functionalized ethylene-methyl acrylate copolymer is 250-350 g / eq, which is used to undergo an in-situ crosslinking reaction with the sulfonic acid groups of the sulfonated polyethersulfone microspheres during processing to form a sea-island type reinforced network structure.

[0011] Furthermore, the sulfonated polyethersulfone microspheres have a particle size of 0.5-2 μm and a degree of sulfonation of 30-50%. In the material, they act as ion conductivity inhibitors to improve volume resistivity and participate in the pyrolysis char formation process to improve char residue.

[0012] Furthermore, the mass ratio of Mg(OH)2 to Al2O3 in the nano-magnesium hydroxide / alumina composite filler is 3:1 to 5:1, and the surface is coated with zinc stearate, which has the functions of endothermic decomposition flame retardancy, smoke suppression and improved dielectric properties.

[0013] Furthermore, the anti-corona agent is composed of nano-titanium dioxide / boron nitride core-shell structured particles with an average particle size ≤100nm.

[0014] Furthermore, the polyol char-forming promoter is pentaerythritol or dipentaerythritol, which synergistically generates an intumescent char layer with the phosphorus-containing flame retardant during combustion, with a limiting oxygen index ≥35%.

[0015] This invention discloses a method for preparing flame-retardant wire insulation material for distribution cabinet wiring, using any of the flame-retardant wire insulation materials for distribution cabinet wiring as described above, comprising the following steps:

[0016] (1) Add each component to a high-speed mixer according to the proportion and mix at 80-100℃ for 8-15 minutes to obtain a premix;

[0017] (2) Add the premixed material to a twin-screw extruder and melt-blend and extrude granulate at a temperature of 190-240℃ and a screw speed of 250-320rpm;

[0018] (3) After drying, the obtained granules are coated onto a copper conductor using an electric wire extruder and then cross-linked and shaped by irradiation to obtain the finished electric wire.

[0019] Furthermore, in step (3), electron beam irradiation is used for crosslinking at a dose of 80-120 kGy to form a three-dimensional network structure in the material, thereby increasing the heat distortion temperature to above 120°C.

[0020] Furthermore, the wires manufactured using the method for preparing flame-retardant wire insulation materials for distribution cabinet wiring meet the following performance indicators:

[0021] Flame retardancy rating of UL94V-0, limiting oxygen index ≥35%, volume resistivity ≥1×10 15 Ω·cm, heat aging resistance tensile strength retention rate ≥95%, bundled combustion smoke density ≤40%, halogen acid gas release ≤5mg / g.

[0022] The beneficial effects of this invention are:

[0023] The electrical wire insulation material of this invention possesses excellent flame retardant safety and environmental friendliness. Through the synergistic effect of a phosphorus-nitrogen-silicon ternary flame retardant and a polyol char-forming promoter, the material achieves a UL94V-0 flame retardant rating with a limiting oxygen index of 35%-39%, and can rapidly form a dense, expanded char layer to inhibit flame spread. The nano-magnesium hydroxide / alumina composite filler further reduces combustion hazards, with bundled combustion smoke density controlled at 32%-38% and halogen acid gas release as low as 3.5-4.8 mg / g. In electrical fire scenarios, it can reduce toxic fumes and corrosive gases, providing protection for personnel evacuation and equipment, and fully complies with halogen-free environmental protection requirements.

[0024] The material possesses excellent electrical insulation properties and long-term aging resistance, making it suitable for the harsh operating conditions of distribution cabinets. The island-type network structure formed by sulfonated polyethersulfone microspheres and epoxy functionalized copolymers maintains a volume resistivity of 1.2 × 10⁻⁶. 15 -4.8×10 15Ω・cm, combined with nano titanium dioxide / boron nitride core-shell anti-corona agent, enhances resistance to electrical tracking; after 135℃×168h heat aging test, the tensile strength retention rate reaches 95%-98%, and the three-dimensional network formed by irradiation cross-linking can withstand high temperature and voltage stress in the cabinet for a long time, reduce leakage and corona faults, extend wire life, and ensure stable operation of power distribution system.

[0025] This invention balances performance and process practicality, possessing industrialization value. The melt flow rate of the modified PBT matrix is ​​suitable for extrusion processing, and both twin-screw melt blending and electron beam irradiation crosslinking are mature technologies that can be mass-produced without special equipment. The overall material properties are suitable for the wiring requirements of distribution cabinets with rated voltages of 0.6 / 1kV and below. While achieving high flame retardancy, high insulation, and high aging resistance, it does not sacrifice processing convenience, providing a feasible solution that balances performance and cost for the safety upgrade of distribution cabinet wires. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a flame-retardant wire insulation material and its preparation method for wiring in a distribution cabinet, as described in this application. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions in the specific embodiments of the present invention will be clearly and completely described below.

[0028] This invention discloses a high-safety halogen-free flame-retardant wire insulation material for internal wiring in distribution cabinets, which is made of the following components in parts by weight:

[0029] The composition includes: 40-55 parts modified polybutylene terephthalate matrix resin, 8-12 parts phosphorus-nitrogen-silicon ternary synergistic flame retardant, 6-10 parts epoxy-functionalized ethylene-methyl acrylate copolymer, 4-7 parts sulfonated polyethersulfone microspheres, 10-15 parts nano magnesium hydroxide / alumina composite filler, 1-3 parts anti-corona agent, 0.5-1.2 parts heat stabilizer, 0.3-0.8 parts lubricant, 0.6-1.0 parts silane coupling agent, and 0.5-1.5 parts polyol char formation accelerator.

[0030] Among them, the modified polybutylene terephthalate matrix resin is a copolyester with hydroxyl-terminated end-capped and flexible aliphatic segments introduced, and the melt flow rate is 8-15 g / 10 min.

[0031] This invention uses modified polybutylene terephthalate (PET) with terminal hydroxyl groups and introduced flexible aliphatic segments as the matrix resin. This modification treatment improves the resin's thermal stability and hydrolysis resistance through the end-capping reaction. Simultaneously, the introduced flexible segments effectively regulate the polymer's crystallization behavior and molecular chain mobility, stabilizing its melt flow rate within the ideal processing range of eight to fifteen grams per ten minutes. This ensures the material possesses excellent processing rheological properties in subsequent wire extrusion coating processes, laying the foundation for forming a dense and uniform insulation layer.

[0032] The phosphorus-nitrogen-silicon ternary synergistic flame retardant in the formulation exhibits a dual flame-retardant mechanism in both the gas and condensed phases upon heating, synergistically catalyzing the formation of an expanded char layer with the polyol char-forming promoter. The nano-magnesium hydroxide and alumina composite filler undergoes staged endothermic dehydration during combustion, lowering the system temperature and diluting combustible gases; high-shear pre-dispersion is employed during mixing. Simultaneously, the epoxy-functionalized ethylene methyl acrylate copolymer and sulfonated polyethersulfone microspheres undergo an in-situ reaction under processing heat, constructing an island-type network structure that not only inhibits the migration of conductive ions but also enhances the char layer strength, thus collectively endowing the material with an extremely high limiting oxygen index and excellent UL94V0 flame retardant performance.

[0033] The nano-sized magnesium hydroxide-alumina composite filler, after being coated with zinc stearate, exhibits improved compatibility with the polymer matrix. Its uniform dispersion in the system effectively enhances the material's resistance to tracking. Special anti-corona agent particles inhibit the development of partial discharge channels, while silane coupling agents further strengthen the bonding forces between interfaces. Combined with the effects of heat stabilizers and lubricants, the material ultimately maintains high volume resistivity while possessing excellent mechanical strength, heat aging resistance, and processing stability, fully meeting the insulation material requirements for internal wiring in 0.6 / 1kV and below distribution cabinets.

[0034] As one implementation method, the phosphorus-nitrogen-silicon ternary synergistic flame retardant is a cage-type silsesquioxane derivative grafted with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, with a phosphorus content ≥8wt% and a silicon content ≥12wt%.

[0035] One embodiment of the present invention employs a phosphorus-nitrogen-silicon ternary synergistic flame retardant with a well-defined molecular structure. This flame retardant is a derivative formed by successfully grafting 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide onto a cage-like silsesquioxane skeleton. Through controlled chemical reactions such as hydrosilylation or esterification, the phosphaphenanthrene flame-retardant units are firmly bonded covalently to a rigid organic-inorganic hybrid cage-like molecular structure, thereby constructing a synergistic flame-retardant system with closely adjacent phosphorus and silicon elements at the molecular scale.

[0036] This unique molecular structure enables it to exhibit outstanding ternary synergistic flame retardant properties when heated or burned. The phosphaphenanthrene units bonded to the cage-like siloxane efficiently capture free radicals required for the combustion chain reaction in the gas phase, while simultaneously promoting the dehydration and char formation of the polymer matrix in the condensed phase. At the same time, the stable siloxane cage structure rapidly migrates to the material surface at high temperatures and reconstructs into a robust silicon-carbon ceramic thermal insulation layer. This layer effectively isolates heat and mass transfer, thus achieving a unified approach to gas-phase and condensed-phase flame retardancy.

[0037] This flame retardant derivative requires a phosphorus content of no less than 8% and a silicon content of no less than 12% to ensure a sufficiently high concentration of effective flame-retardant elements in the composite. Its chemically bonded molecular structure avoids the migration and precipitation problems of traditional physically blended flame retardants, resulting in better compatibility with the polymer matrix. Ultimately, this agent imparts excellent flame-retardant properties to the material while significantly reducing its negative impact on the material's mechanical and electrical insulation properties, achieving high safety and long service life for wire insulation materials.

[0038] As one implementation method, the epoxy equivalent in the epoxy-functionalized ethylene-methyl acrylate copolymer is 250-350 g / eq, which is used to undergo an in-situ crosslinking reaction with the sulfonic acid groups of the sulfonated polyethersulfone microspheres during processing to form an island-type reinforced network structure.

[0039] One embodiment of the present invention uses an epoxy-functionalized ethylene methyl acrylate copolymer with an epoxy equivalent ranging from 250 to 350 g / m³. This epoxy equivalent range is designed to ensure that the epoxy groups carried on the copolymer chains have suitable reactivity under the temperature conditions of melt blending. When co-existing with sulfonated polyethersulfone microspheres in the polymer melt, these epoxy groups can undergo efficient and controllable ion exchange and ring-opening addition chemical reactions with the sulfonic acid groups on and within the microspheres.

[0040] This chemical reaction process enables the construction of a unique island-type reinforcing network structure within the matrix resin. Sulfonated polyethersulfone microspheres serve as the dispersed phase, i.e., the islands, while the in-situ generated crosslinks act as strong anchoring points, tightly connecting the microspheres to the epoxy functionalized copolymer and the entire resin matrix into a unified whole. This three-dimensional network, constructed in-situ during processing through a chemical reaction, differs from simple physical blending; it forms a robust microscopic reinforcing framework, significantly limiting polymer chain slippage.

[0041] Firstly, as a highly efficient stress transfer framework, it significantly improves the material's mechanical strength, modulus, and creep resistance. Secondly, this three-dimensional network effectively confines polymer chain movement and suppresses carrier migration paths, thereby significantly increasing the material's volume resistivity and inhibiting electrical dendrite growth. Finally, this structural design enables the material to achieve both reinforcement and superior thermal stability and partial discharge resistance, fully meeting the requirements for high-safety wire insulation materials.

[0042] In one implementation method, the sulfonated polyethersulfone microspheres have a particle size of 0.5-2 μm and a degree of sulfonation of 30-50%. In the material, they act as ion conductivity inhibitors to increase volume resistivity and participate in the pyrolysis char formation process to increase the char residue rate.

[0043] One embodiment of the present invention precisely defines the key parameters of sulfonated polyethersulfone microspheres, controlling the particle size between 0.5 and 2 micrometers and maintaining the degree of sulfonation within the range of 30% to 50%. The particle size distribution ensures that the microspheres achieve uniform physical dispersion in the matrix resin, forming a suitable phase interface region. The appropriate degree of sulfonation endows the microspheres with abundant sulfonate groups; these highly polar functional groups can effectively capture and firmly bind any mobile ions that may exist in the material system through strong Coulomb forces.

[0044] The binding mechanism of mobile ions makes sulfonated polyethersulfone microspheres an excellent inhibitor of ionic conductivity. Under the influence of an electric field, the fixed ions cannot migrate long distances to form conductive pathways, thus significantly reducing the leakage current of the material. This directly leads to an increase in the volume resistivity of the material, ensuring that the insulating layer maintains stable and reliable high insulation performance under long-term voltage, reducing the risk of failure due to current leakage.

[0045] Meanwhile, sulfonated polyethersulfone microspheres exhibit a second key function when the material faces high temperatures or open flame threats. The inherent rigid sulfone bonds in their molecular structure provide excellent thermal stability, while the sulfonic acid groups act as acidic catalysts in the early stages of pyrolysis, promoting intramolecular and intermolecular crosslinking and aromatization reactions within the polymer matrix and the microspheres themselves. The catalytic char formation process increases the amount and density of residual char after high-temperature pyrolysis, and the resulting continuous and robust char layer effectively blocks the transfer of heat and combustible gases, thereby synergistically improving the overall flame retardant rating and fire safety of the material.

[0046] As one implementation method, the mass ratio of Mg(OH)2 to Al2O3 in the nano magnesium hydroxide / alumina composite filler is 3:1 to 5:1, and the surface is coated with zinc stearate, which has the functions of endothermic decomposition flame retardancy, smoke suppression and improved dielectric properties.

[0047] This embodiment constructs a tiered synergistic flame retardant system by precisely controlling the mass ratio of nano-magnesium hydroxide to alumina between 3:1 and 5:1. In the process, nano-sized magnesium hydroxide and alumina particles are premixed according to this ratio. Mechanical stirring ensures that the two particles are initially evenly dispersed. Utilizing their different thermal decomposition characteristics, they complement each other. Magnesium hydroxide decomposes at a lower temperature, releasing water of crystallization and absorbing a large amount of heat, rapidly reducing the surface and internal temperature of the material. Simultaneously, the water vapor dilutes the concentration of surrounding combustible gases. Alumina, on the other hand, maintains structural stability at higher temperatures, continuously absorbing heat and inhibiting further pyrolysis of the material. This tiered heat absorption mechanism improves flame retardant efficiency, avoiding the problem of single flame retardant fillers failing within a specific temperature range. Furthermore, the decomposition products are all inorganic and harmless substances, reducing the generation of harmful smoke during combustion and mitigating the smoke hazard in fires from the source.

[0048] To address the issues of easy agglomeration and poor compatibility with polymer matrices in nanofillers, this embodiment employs zinc stearate to surface-coat the composite filler. Specifically, zinc stearate is dissolved in a suitable solvent, and a premixed nano-magnesium hydroxide / alumina composite filler is added. The mixture is stirred at a specific temperature and maintained for a period of time, allowing zinc stearate molecules to uniformly adhere to the surface of the filler particles through physical adsorption and chemical reactions, forming a dense coating layer. Finally, the solvent is removed by drying, yielding the surface-modified composite filler. This process reduces the surface energy of the nanoparticles, effectively preventing particle agglomeration and ensuring uniform dispersion during subsequent mixing with the matrix resin. Simultaneously, the organic segments of zinc stearate can interact with the polymer molecular chains, enhancing the interfacial bonding between the filler and the resin. This prevents a decline in the material's mechanical properties due to uneven filler dispersion, allowing the composite filler to perform its function without compromising the overall structural stability of the material.

[0049] The nano-magnesium hydroxide / alumina composite filler in this embodiment achieves a multi-functional synergy of heat absorption and flame retardancy, smoke suppression, and improved dielectric properties through a dual design of optimized formulation and surface modification. In addition to its flame retardant and smoke suppression functions, the uniformly dispersed composite filler also enhances insulation. Both magnesium hydroxide and alumina are highly insulating inorganic materials; their nano-particles form a microscopic insulating network within the matrix resin, blocking potential conductive pathways within the material and reducing ion migration, thereby improving the material's volume resistivity and tracking resistance. Simultaneously, the zinc stearate coating reduces the polarization effect at the filler-resin interface, lowering dielectric loss. This multi-functional synergistic design allows the material to simultaneously meet the stringent requirements of distribution cabinet wires for flame retardancy, environmental friendliness, and electrical insulation without the need for multiple single-function additives. It simplifies the formulation system while ensuring stable overall performance during long-term use, adapting to the complex high-temperature, high-voltage working environment inside distribution cabinets.

[0050] As one implementation method, the anti-corona agent is nano-titanium dioxide / boron nitride core-shell structured particles with an average particle size ≤100nm, used to improve the material's resistance to tracking index (CTI≥600V) under partial discharge environment.

[0051] The implementation method employs a nano-anti-corona agent with a unique core-shell structure. This composite particle consists of titanium dioxide as the core and boron nitride as the outer shell, with the average particle size strictly controlled to below 100 nanometers. Firstly, the nanoscale effect provides a large specific surface area and interfacial effect. More importantly, this core-shell structure, achieved through chemical or physical methods, uniformly coats the outer surface of the titanium dioxide nanoparticles with a boron nitride shell, achieving a perfect combination and functional complementarity of the two materials' properties.

[0052] When the material is in a harsh environment with high electric fields and partial discharge, the core-shell structured particles play a crucial protective role. The outer boron nitride coating, with its excellent insulating properties and layered structure, constructs microscopic barrier layers within the polymer matrix, effectively dispersing the electric field intensity and hindering the extension and development of discharge channels. Simultaneously, the internal titanium dioxide core contributes its high dielectric constant and thermal stability, helping to dissipate locally concentrated charges and heat, thereby synergistically suppressing the formation of conductive carbonization pathways.

[0053] The introduction of these nano-sized boron nitride titanium dioxide core-shell particles enhances the material's resistance to electrical tracking. This makes it difficult for continuous, conductive carbonization marks to form on the surface of the insulating material, even under high voltage stress and repeated partial discharge impacts. This significantly increases the material's tracking resistance index to 600 volts or even higher, ensuring that the wires can withstand corona discharge erosion for extended periods in the compact space of distribution cabinets and potentially polluted environments, thus enhancing the reliability and service life of the insulation system.

[0054] As one implementation method, the polyol char-forming promoter is pentaerythritol or dipentaerythritol, which synergistically generates an intumescent char layer with phosphorus-containing flame retardants during combustion, with a limiting oxygen index ≥35%.

[0055] Polyhydroxy compounds can serve as excellent carbon sources at high temperatures, and the abundant hydroxyl groups in their molecular structure provide the necessary structural basis for the formation of a dense carbon layer. When the material is exposed to a flame, it first undergoes a melting process, covering the polymer surface and preparing for the subsequent expansion and charring reaction.

[0056] Its function lies in its excellent synergistic effect with the phosphorus-based components in phosphorus-nitrogen-silicon ternary flame retardants. Under heating conditions, the flame retardant decomposes and releases acidic substances such as phosphoric acid and polyphosphoric acid. These acidic products can catalyze the polyol molecules to undergo vigorous dehydration, cross-linking, and aromatization reactions. The catalytic process rapidly constructs a rigid carbonaceous framework with a three-dimensional network structure, while the water vapor and non-flammable gases released in the reaction are encapsulated in the forming viscous melt.

[0057] The thermal expansion of the gas causes the viscous carbonaceous skeleton to rapidly expand, ultimately forming a significantly thick, structurally stable, and closed-cell porous foamed expanded carbon layer on the material surface. This carbon layer acts as a highly efficient thermal and oxygen barrier, effectively preventing external heat from transferring into the matrix and inhibiting the escape of combustible decomposition products. This expansion and flame-retardant mechanism, working synergistically with other components, elevates the material's limiting oxygen index to an excellent level of no less than 35%, thus achieving outstanding flame-retardant performance.

[0058] This invention discloses a method for preparing electrical insulation material for power distribution cabinets, which includes the following steps:

[0059] 1. Add each component to a high-speed mixer according to the proportions, and mix at 80-100℃ for 8-15 minutes to obtain a premix;

[0060] 2. Add the premixed material to a twin-screw extruder and melt-blend, then extrude and granulate at a temperature of 190-240℃ and a screw speed of 250-320rpm.

[0061] After drying, the obtained granules are coated onto a copper conductor using an electric wire extruder, and then cross-linked and shaped by irradiation to obtain the finished electric wire.

[0062] The first step in the preparation method of this invention is to achieve sufficient pre-dispersion and interface pretreatment of the raw material components. Weighed modified polybutylene terephthalate matrix resin, phosphorus-nitrogen-silicon ternary synergistic flame retardant, epoxy-functionalized ethylene methyl acrylate copolymer, sulfonated polyethersulfone microspheres, nanocomposite fillers, and other functional additives are added to a high-speed mixer. Mechanical stirring is performed for eight to fifteen minutes at a temperature of 80 to 100 degrees Celsius. This not only achieves preliminary macroscopic uniform mixing of the components, but more importantly, the heat softens the resin and activates the silane coupling agent, enabling it to effectively coat and modify the surface of the nanofiller, laying a uniform material foundation for subsequent melt blending.

[0063] The core of the second step lies in achieving molecular-level compatibility and in-situ reaction through melt blending. The premixed material is fed into a co-rotating twin-screw extruder. Within a set temperature range and screw speed, the material undergoes melting, shearing, and conveying from the feeding section to the homogenization section. During this process, an in-situ crosslinking reaction occurs between the epoxy functionalized copolymer and the sulfonated polyethersulfone microspheres, initiating the construction of an island-type network structure. Simultaneously, the molten resin matrix uniformly coats and disperses various nanofillers and functional additives, forming a homogeneous polymer blend system. Finally, through die extrusion, cooling, and pelletizing, a stable composite material masterbatch is obtained.

[0064] The third step completes the molding and final structural shaping of the insulation layer. The dried granules are fed into a wire extruder, where, under precisely controlled temperature and traction speed, the molten composite material is uniformly coated onto the surface of the copper conductor to form an insulation layer. Subsequently, the insulation layer undergoes post-treatment using radiation cross-linking, a process that induces further formation of a three-dimensional network cross-linked structure between the polymer molecular chains. This network structure significantly enhances the insulation layer's resistance to heat deformation, mechanical strength, and long-term stability, resulting in a high-safety finished wire that fully meets the requirements for voltage levels of 0.6 kV and below.

[0065] In one implementation method, step 3 uses electron beam irradiation crosslinking with a dose of 80-120 kGy to form a three-dimensional network structure in the material, thereby increasing the heat distortion temperature to above 120°C.

[0066] One embodiment of the present invention employs electron beam irradiation crosslinking technology in the wire insulation layer shaping process. This technology utilizes a high-energy electron beam to penetrate the insulation material. The energy of the beam is absorbed by the polymer molecular chains, sufficient to break the low-energy chemical bonds (such as carbon and hydrogen bonds) within the molecular chains, thereby uniformly generating a large number of highly reactive free radicals throughout the material. These free radicals are randomly generated within the material, providing the necessary reaction starting point for the subsequent formation of a three-dimensional network structure.

[0067] At a set irradiation dose of 80 to 120 kilogras, these newly generated free radicals rapidly couple with each other, establishing strong and permanent carbon-carbon cross-links between the originally linear polymer molecular chains and between the matrix resin and reactive components. These cross-links are interconnected in space, forming a three-dimensional network macromolecular structure that runs throughout the entire insulating material. This process does not rely on high temperatures or chemical initiators, making it a highly efficient and clean chemical modification method.

[0068] The resulting three-dimensional network structure fundamentally improves the macroscopic properties of the material. It restricts the slippage and movement of polymer molecular chains under thermal energy, thereby raising the material's heat distortion temperature to over 120 degrees Celsius. This transformation endows the wire insulation layer with excellent resistance to short-term thermal shock and long-term heat aging, ensuring the dimensional stability and electrical insulation reliability of the wires inside the distribution cabinet under high-temperature conditions, and extending the product's service life.

[0069] As one implementation method, the wires made of the insulation material of the distribution cabinet wires meet the following performance indicators:

[0070] Flame retardancy rating of UL94V-0, limiting oxygen index ≥35%, volume resistivity ≥1×10 15 Ω·cm, heat aging resistance (135℃×168h) tensile strength retention rate ≥95%, bundled combustion smoke density ≤40%, halogen acid gas release ≤5mg / g, suitable for internal connection of distribution cabinets with rated voltage of 0.6 / 1kV and below.

[0071] The wire manufactured using this invention achieves the highest industry standards in terms of flame retardant safety. Its superior flame retardant performance is attributed to the highly efficient synergy between a phosphorus-nitrogen-silicon ternary flame retardant and a polyol char-forming promoter, which rapidly forms a dense, expanded char layer in the flame, achieving a UL94V0 flame retardant rating while maintaining a limiting oxygen index of over 35%. The sulfonated polyethersulfone microspheres, acting as an ionic conductivity inhibitor, and the island-type network structure formed by the epoxy functionalized copolymer, together ensure excellent insulation performance with a volume resistivity of not less than 10 to the power of 15 ohm-cm.

[0072] This wire exhibits excellent thermal stability and environmental safety. After undergoing a 168-hour thermal aging test at 135 degrees Celsius, its tensile strength retention rate remains above 95%, thanks to the stable structure of the modified polybutylene terephthalate matrix and the three-dimensional network formed by radiation cross-linking. The tiered flame retardant and smoke-suppressing functions of the nanocomposite filler reduce the smoke density during bundled combustion to below 40%, and all components meet the halogen-free requirement, with halogen acid gas release strictly controlled to within 5 milligrams per gram.

[0073] These comprehensive performance indicators ensure that the wire is fully suitable for internal connection scenarios in various distribution cabinets with rated voltages of 0.6 / 1kV and below. It not only effectively resists the risk of electrical fires that may occur inside the cabinet, but also withstands long-term high-temperature operating environments, maintaining low-smoke, halogen-free safety characteristics in the event of electrical faults. This provides material assurance for the safe and reliable operation of the power distribution system, fully demonstrating the high-safety design concept and practical value of this invention.

[0074] Performance tests are conducted in accordance with industry standards: UL94 (flame retardancy rating), oxygen index method (limiting oxygen index, LOI), high resistance meter method (volume resistivity), 135℃×168h heat aging test (tensile strength retention rate), GB / T17651 (bundle burning smoke density), and IEC60754-2 (halogen acid gas release).

[0075] I. Implementation Examples

[0076] Example 1

[0077] The high-safety halogen-free flame-retardant wire insulation material used in Example 1 is made from the following components by weight: 45 parts of modified polybutylene terephthalate matrix resin (the resin is end-capped with hydroxyl groups and introduced with flexible aliphatic segments, with a melt flow rate of 10 g / 10 min), 10 parts of a phosphorus-nitrogen-silicon ternary synergistic flame retardant (a cage-like silsesquioxane derivative grafted with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, with a phosphorus content of 9 wt% and a silicon content of 13 wt%), epoxy functionalized... The composition includes 8 parts of ethylene-methyl acrylate copolymer (epoxy equivalent 300 g / eq), 5 parts of sulfonated polyethersulfone microspheres (particle size 1 μm, sulfonation degree 40%), 12 parts of nano-magnesium hydroxide / alumina composite filler (mass ratio 4:1, surface coated with zinc stearate), 2 parts of anti-corona agent (nano-titanium dioxide / boron nitride core-shell structure particles, average particle size 80 nm), 0.8 parts of heat stabilizer, 0.5 parts of lubricant, 0.8 parts of silane coupling agent, and 1.0 part of polyol char-forming promoter (pentaerythritol). The preparation process is as follows: Each component is added to a high-speed mixer according to the specified ratio and mixed at 90℃ for 12 minutes to obtain a premix; the premix is ​​fed into a twin-screw extruder and melt-blended and extruded into granules at 210℃ and 280 rpm; after drying, the granules are coated onto a copper conductor using a wire extruder and then cross-linked and shaped by 100 kGy electron beam irradiation. The wires made from this insulating material have the following properties: flame retardant rating UL94V-0, limiting oxygen index 37%, and volume resistivity 2.5×10⁻⁶. 15 Ω・cm, heat aging tensile strength retention rate 97%, bundled combustion smoke density 35%, halogen acid gas release 4.2mg / g.

[0078] Example 2

[0079] The insulating material components of Example 2, by weight, are as follows: 40 parts of modified polybutylene terephthalate matrix resin (terminated with hydroxyl groups + flexible aliphatic segments, melt flow rate 8 g / 10 min), 8 parts of phosphorus-nitrogen-silicon ternary synergistic flame retardant (phosphorus content 8 wt%, silicon content 12 wt%), 6 parts of epoxy-functionalized ethylene-methyl acrylate copolymer (epoxy equivalent 250 g / eq), 4 parts of sulfonated polyethersulfone microspheres (particle size 0.5 μm, sulfonation degree 30%), 10 parts of nano-magnesium hydroxide / alumina composite filler (mass ratio 3:1, coated with zinc stearate), 1 part of anti-corona agent (particle size 50 nm), 0.5 parts of heat stabilizer, 0.3 parts of lubricant, 0.6 parts of silane coupling agent, and 0.5 parts of polyol char-forming promoter (dipentaerythritol). The preparation process is as follows: premixed material is prepared by mixing at 80℃ for 8 minutes; twin-screw extrusion parameters are 190℃, 250rpm, and irradiation dose is 80kGy. Performance indicators are: flame retardant rating UL94V-0, limiting oxygen index 35%, and volume resistivity 1.2×10⁻⁶. 15 Ω・cm, heat aging tensile strength retention rate 95%, bundled combustion smoke density 38%, halogen acid gas release 4.8mg / g.

[0080] Example 3

[0081] The insulating material components of Example 3, by weight, are as follows: 55 parts modified polybutylene terephthalate matrix resin (melt flow rate 15 g / 10 min), 12 parts phosphorus-nitrogen-silicon ternary synergistic flame retardant (phosphorus content 10 wt%, silicon content 14 wt%), 10 parts epoxy-functionalized ethylene-methyl acrylate copolymer (epoxy equivalent 350 g / eq), 7 parts sulfonated polyethersulfone microspheres (particle size 2 μm, sulfonation degree 50%), 15 parts nano-magnesium hydroxide / alumina composite filler (mass ratio 5:1, zinc stearate coating), 3 parts anti-corona agent (particle size 100 nm), 1.2 parts heat stabilizer, 0.8 parts lubricant, 1.0 part silane coupling agent, and 1.5 parts polyol char formation promoter (pentaerythritol). The preparation process is as follows: premixed material is prepared by mixing at 100°C for 15 minutes; twin-screw extrusion parameters are 240°C, 320 rpm, and irradiation dose is 120 kGy. Performance specifications are: UL94V-0 flame retardant rating, limiting oxygen index 39%, and volume resistivity 4.8 × 10⁻⁶. 15 Ω・cm, the retention rate of thermal aging tensile strength can reach 98% under strict temperature control conditions, with a typical value of ≥95%, the smoke density of bundled combustion is 32%, and the release of halogen acid gas is 3.5mg / g.

[0082] Example 4

[0083] The insulating material components of Example 4, by weight, are as follows: 50 parts modified polybutylene terephthalate matrix resin (melt flow rate 12 g / 10 min), 11 parts phosphorus-nitrogen-silicon ternary synergistic flame retardant (phosphorus content 9.5 wt%, silicon content 13.5 wt%), 9 parts epoxy-functionalized ethylene-methyl acrylate copolymer (epoxy equivalent 320 g / eq), 6 parts sulfonated polyethersulfone microspheres (particle size 1.5 μm, sulfonation degree 45%), 13 parts nano magnesium hydroxide / alumina composite filler (mass ratio 4.5:1, zinc stearate coating), 2.5 parts anti-corona agent (particle size 90 nm), 1.0 part heat stabilizer, 0.6 parts lubricant, 0.9 parts silane coupling agent, and 1.2 parts polyol char formation promoter (dipentaerythritol). The preparation process is as follows: premixed material is prepared by mixing at 95℃ for 10 minutes; twin-screw extrusion parameters are 220℃ and 300 rpm; irradiation dose is 110 kGy. Performance indicators are: flame retardant rating UL94V-0, limiting oxygen index 38%, and volume resistivity 3.6 × 10⁻⁶. 15 Ω・cm, heat aging tensile strength retention rate 96%, bundled combustion smoke density 34%, halogen acid gas release 3.8mg / g.

[0084] Example 5

[0085] The insulating material components of Example 5, by weight, are as follows: 48 parts of modified polybutylene terephthalate matrix resin (melt flow rate 13 g / 10 min), 9 parts of phosphorus-nitrogen-silicon ternary synergistic flame retardant (phosphorus content 8.5 wt%, silicon content 12.5 wt%), 7 parts of epoxy-functionalized ethylene-methyl acrylate copolymer (epoxy equivalent 280 g / eq), 5.5 parts of sulfonated polyethersulfone microspheres (particle size 0.8 μm, sulfonation degree 35%), 14 parts of nano-magnesium hydroxide / alumina composite filler (mass ratio 3.5:1, zinc stearate coating), 1.5 parts of anti-corona agent (particle size 70 nm), 0.9 parts of heat stabilizer, 0.4 parts of lubricant, 0.7 parts of silane coupling agent, and 0.8 parts of polyol char-forming promoter (pentaerythritol). The preparation process is as follows: premixed material is prepared by mixing at 85℃ for 13 minutes; twin-screw extrusion parameters are 200℃ and 260 rpm; irradiation dose is 90 kGy. Performance indicators are: flame retardant rating UL94V-0, limiting oxygen index 36%, volume resistivity 2.1 × 10⁻⁶. 15 Ω・cm, heat aging tensile strength retention rate 95.5%, bundled combustion smoke density 36%, halogen acid gas release 4.5mg / g.

[0086] II. Comparative Example

[0087] Comparative Example 1 (Ordinary PBT replacing modified PBT)

[0088] Comparative Example 1 aims to verify the necessity of modifying the matrix resin. The modified polybutylene terephthalate (PPT) in Example 1 was replaced with ordinary PPT (without hydroxyl end caps, without flexible aliphatic segments, melt flow rate of 10 g / 10 min), with the amount remaining at 45 parts. The types, amounts, and preparation processes of other components were completely consistent with Example 1. The insulation material prepared in this comparative example exhibited the following properties: flame retardancy rating only UL94V-1, limiting oxygen index 32%, and volume resistivity 8.5 × 10¹. 4 The thermal aging tensile strength retention rate was 88%, the bundled combustion smoke density was 45%, and the halogen acid gas release was 4.3 mg / g. The core reason for the performance degradation is that ordinary PBT has poor thermal stability and hydrolysis resistance, and insufficient molecular chain mobility, which prevents it from synergistically forming a dense insulating layer and a stable expanded carbon layer with flame retardants, fillers, and other components, resulting in a comprehensive decline in flame retardant, insulating, and thermal aging properties.

[0089] Comparative Example 2 (insufficient flame retardant and failure to meet key element standards)

[0090] Comparative Example 2 deviates from the requirements for flame retardant content and composition in the abstract. The amount of the phosphorus-nitrogen-silicon ternary synergistic flame retardant in Example 1 is reduced to 6 parts, and the phosphorus content of this flame retardant is only 7 wt% and the silicon content is 10 wt% (both lower than the 8 wt% and 12 wt% specified in the abstract). Other components and preparation processes are the same as in Example 1. Its performance indicators are: flame retardant rating UL94V-2, limiting oxygen index 31%, and volume resistivity 1.8 × 10⁻⁶. 15 The performance defects stem from insufficient flame retardant content and inadequate concentration of effective elements (phosphorus and silicon), resulting in weakened gas-phase free radical capture ability, reduced char formation efficiency in the condensed phase, and significantly deteriorated flame retardant and smoke suppression performance, failing to meet the safety requirements of electrical distribution cabinet wires. The flame retardant content is Ω・cm, the heat aging tensile strength retention rate is 96%, the bundled combustion smoke density is 52%, and the halogen acid gas release is 3.9 mg / g.

[0091] Comparative Example 3 (non-epoxy functionalized copolymer, replaced with ordinary copolymer)

[0092] Comparative Example 3 omits the epoxy-functionalized ethylene-methyl acrylate copolymer from the abstract and replaces it with a regular ethylene-methyl acrylate copolymer (without epoxy groups, unable to undergo in-situ crosslinking). The amount remains 8 parts, and the other components and preparation process are the same as in Example 1. Its properties are: flame retardant rating UL94V-1, limiting oxygen index 33%, and volume resistivity 6.2×10¹. 4The thermal aging tensile strength retention rate was 90%, the bundled combustion smoke density was 48%, and the halogen acid gas release was 4.1 mg / g. The performance degradation was due to the inability of ordinary copolymers to form a sea-island type reinforced network structure with sulfonated polyethersulfone microspheres. This resulted in the inability to effectively suppress ionic conductivity (leading to a decrease in volume resistivity) and to enhance the char layer strength (affecting flame retardancy). At the same time, the thermal stability of the material decreased due to the lack of cross-linking support.

[0093] Comparative Example 4 (irradiation dose below the statutory limit)

[0094] Comparative Example 4 adjusted the irradiation parameters in the preparation process, reducing the electron beam irradiation dose of Example 1 to 60 kGy (lower than the required 80-120 kGy). Other components and process steps remained identical to Example 1. Its properties were: flame retardant rating UL94V-1, limiting oxygen index 34%, and volume resistivity 1.5 × 10⁻⁶. 15 The thermal aging tensile strength retention rate was 89%, the bundled combustion smoke density was 43%, and the halogen acid gas release was 4.0 mg / g. The key to the performance degradation was insufficient irradiation dose, which prevented the material from forming a complete three-dimensional network structure. This led to easy slippage of molecular chains at high temperatures, a decrease in heat distortion temperature, and a decline in thermal aging stability and char layer integrity, ultimately affecting flame retardancy and mechanical properties.

[0095] Comparative Example 5 (Deviation of Composite Packing Ratio)

[0096] Comparative Example 5 altered the ratio of nano-magnesium hydroxide / alumina composite filler, adjusting the mass ratio to 2:1 (lower than the summary-defined 3:1-5:1), while maintaining the same dosage of 12 parts and surface coating with zinc stearate. Other components and preparation processes remained consistent with Example 1. Its properties were: flame retardant rating UL94V-1, limiting oxygen index 33%, and volume resistivity 1.3 × 10⁻⁶. 15 The performance defects stem from several factors: Ω·cm, 92% retention of thermal aging tensile strength, 47% smoke density during bundled combustion, and 4.4 mg / g release of halogen acid gas. These defects include deviations in filler ratio from the design, failure of the tiered heat absorption and flame retardant mechanism, insufficient magnesium hydroxide content leading to weakened heat absorption and cooling effects at low temperatures, and the inability of alumina to fill the flame retardant gaps in the temperature range, resulting in ineffective dilution of combustible gases and ultimately a decline in both flame retardant and smoke suppression properties.

[0097] III. Performance Comparison Summary

[0098] The test results are shown in Table 1 below.

[0099]

[0100] Table 1

[0101] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A flame-retardant wire insulation material for wiring in distribution cabinets, characterized in that, It is made from the following components in parts by weight: The composition includes: 40-55 parts modified polybutylene terephthalate matrix resin, 8-12 parts phosphorus-nitrogen-silicon ternary synergistic flame retardant, 6-10 parts epoxy-functionalized ethylene-methyl acrylate copolymer, 4-7 parts sulfonated polyethersulfone microspheres, 10-15 parts nano magnesium hydroxide / alumina composite filler, 1-3 parts anti-corona agent, 0.5-1.2 parts heat stabilizer, 0.3-0.8 parts lubricant, 0.6-1.0 parts silane coupling agent, and 0.5-1.5 parts polyol char formation accelerator. Among them, the modified polybutylene terephthalate matrix resin is a copolyester with hydroxyl-terminated end-capped and flexible aliphatic segments introduced, and the melt flow rate is 8-15 g / 10 min.

2. The flame-retardant wire insulation material for distribution cabinet wiring as described in claim 1, characterized in that: The phosphorus-nitrogen-silicon ternary synergistic flame retardant is a cage-type silsesquioxane derivative grafted with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, with a phosphorus content ≥8wt% and a silicon content ≥12wt%.

3. The flame-retardant wire insulation material for distribution cabinet wiring as described in claim 1, characterized in that: The epoxy equivalent in the epoxy-functionalized ethylene-methyl acrylate copolymer is 250-350 g / eq, which is used to undergo an in-situ crosslinking reaction with the sulfonic acid groups of sulfonated polyethersulfone microspheres during processing to form a sea-island type reinforced network structure.

4. The flame-retardant wire insulation material for distribution cabinet wiring as described in claim 1, characterized in that: The sulfonated polyethersulfone microspheres have a particle size of 0.5-2 μm and a degree of sulfonation of 30-50%. In the material, they act as ion conductivity inhibitors to improve volume resistivity and participate in the pyrolysis char formation process to improve char residue.

5. The flame-retardant wire insulation material for distribution cabinet wiring as described in claim 1, characterized in that: The mass ratio of Mg(OH)2 to Al2O3 in the nano magnesium hydroxide / alumina composite filler is 3:1 to 5:1, and the surface is coated with zinc stearate, which has the functions of endothermic decomposition flame retardancy, smoke suppression and improved dielectric properties.

6. The flame-retardant wire insulation material for distribution cabinet wiring as described in claim 1, characterized in that: The anti-corona agent is composed of nano-titanium dioxide / boron nitride core-shell structured particles with an average particle size ≤100nm.

7. The flame-retardant wire insulation material for distribution cabinet wiring as described in claim 1, characterized in that: The polyol char-forming accelerator is pentaerythritol or dipentaerythritol, which synergistically forms an intumescent char layer with phosphorus-containing flame retardants during combustion, with a limiting oxygen index ≥35%.

8. A method for preparing flame-retardant wire insulation material for distribution cabinet wiring, using the flame-retardant wire insulation material for distribution cabinet wiring as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) Add each component to a high-speed mixer according to the proportion and mix at 80-100℃ for 8-15 minutes to obtain a premix; (2) Add the premixed material to a twin-screw extruder and melt-blend and extrude granulate at a temperature of 190-240℃ and a screw speed of 250-320rpm; (3) After drying, the obtained granules are coated onto a copper conductor using an electric wire extruder and then cross-linked and shaped by irradiation to obtain the finished electric wire.

9. A method for preparing a flame-retardant wire insulation material for distribution cabinet wiring as described in claim 8, characterized in that: In step (3), electron beam irradiation is used for crosslinking at a dose of 80-120 kGy to form a three-dimensional network structure in the material and increase the heat distortion temperature to above 120°C.

10. The wire manufactured using the method for preparing flame-retardant wire insulation material for distribution cabinet wiring as described in claim 8, characterized in that, Meet the following performance indicators: Flame retardancy rating of UL94V-0, limiting oxygen index ≥35%, volume resistivity ≥1×10 15 Ω·cm, heat aging resistance tensile strength retention rate ≥95%, bundled combustion smoke density ≤40%, halogen acid gas release ≤5mg / g.

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