An intumescent flame-retardant polyolefin jacketed cable and method of processing

Abstract

The application discloses an intumescent flame-retardant polyolefin sheath cable and a processing method, and belongs to the technical field of wires and cables. The method comprises the following steps: performing surface activity modification on an intumescent flame retardant composed of ammonium polyphosphate, pentaerythritol and melamine to generate an active intumescent flame retardant with active functional groups grafted on the surface; performing reactive melt extrusion on the active intumescent flame retardant, a polyolefin matrix resin and an initiator to obtain a cross-linkable flame-retardant polyolefin composition; coating the cross-linkable flame-retardant polyolefin composition on the outer layer of a conductive wire core and performing cross-linking and curing treatment. Through the surface modification of the flame retardant and the subsequent reactive extrusion and cross-linking and curing process, the flame retardant particles are used as structural pivots in the covalent cross-linking network, the physical filling particles which originally damage the mechanical properties of the matrix are changed into chemical cross-linking nodes of the enhanced network structure, and the technical contradiction between the high filling amount of the flame retardant and the mechanical properties of the polymer matrix is solved.

Description

Technical Field

[0001] This application relates to the field of wire and cable technology, and in particular to an intumescent flame-retardant polyolefin sheathed cable and its processing method. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the performance requirements for high-voltage cables used in vehicles are becoming increasingly stringent. Polyolefin materials are widely used as the base resin for cable sheaths due to their excellent electrical insulation properties, low cost, and ease of processing. However, pure polyolefin materials are highly flammable, and flame-retardant modification is necessary to meet vehicle safety standards. Intumescent Flame Retardant (IFR) systems, due to their low smoke, halogen-free, and low-toxicity environmental characteristics, have become one of the mainstream technologies for polyolefin flame-retardant modification. This system is typically composed of an acid source, a char source, and a gas source, which can form a dense expanded char layer when heated, providing insulation and preventing oxygen deprivation. However, to achieve high levels of flame retardancy (such as UL94 V-0), the amount of intumescent flame retardant added usually needs to reach more than 30 wt%. Such a high inorganic filler loading will severely disrupt the continuity of the polyolefin matrix, leading to a precipitous drop in the material's mechanical properties, especially elongation at break and toughness. Flame retardant particles become stress concentration points within the material, making the cable prone to brittleness during installation and long-term use, posing a serious safety hazard. Existing technology is caught in a fundamental technical contradiction: components added to improve flame retardancy actually compromise the cable's structural reliability. Summary of the Invention

[0003] The first aspect of this application provides a method for processing intumescent flame-retardant polyolefin-sheathed cables, which aims to solve the problem that high-filling-content intumescent flame retardants cause severe degradation of the mechanical properties of the polyolefin sheath in the prior art.

[0004] To address the aforementioned technical problems, this application provides a processing method for an intumescent flame-retardant polyolefin-sheathed cable, comprising: obtaining an active intumescent flame retardant, wherein the active intumescent flame retardant is obtained by surface-active modification of a base intumescent flame retardant, and the surface of the active intumescent flame retardant is grafted with active functional groups; reactively melt-blending the active intumescent flame retardant, a polyolefin matrix resin, and an initiator to obtain a crosslinkable flame-retardant polyolefin composition; coating the crosslinkable flame-retardant polyolefin composition onto the outer surface of a conductive core to form a sheath layer; and performing a crosslinking curing treatment on the sheath layer to form a three-dimensional crosslinked network structure within the sheath layer, wherein the particles of the active intumescent flame retardant serve as crosslinking hubs in the three-dimensional crosslinked network structure.

[0005] Optionally, the basic intumescent flame retardant includes ammonium polyphosphate, a polyol carbon source, and a gas source.

[0006] Optionally, the polyol carbon source is pentaerythritol, and the gas source is melamine.

[0007] Optionally, the surface-active modification treatment includes: reacting the base intumescent flame retardant with a silane coupling agent to graft the active functional group onto the surface of the base intumescent flame retardant; wherein the silane coupling agent contains at least one functional group that can react with the surface groups of the base intumescent flame retardant, as well as the active functional group.

[0008] Optionally, the active functional group is a vinyl group, and the silane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane.

[0009] Optionally, the polyolefin matrix resin includes at least one of ethylene-vinyl acetate copolymer and low-density polyethylene.

[0010] Optionally, the crosslinking curing treatment includes warm water crosslinking curing treatment or irradiation crosslinking curing treatment.

[0011] Optionally, prior to the reactive melt blending, the method further includes: calibrating the rheological properties of the polyolefin matrix resin to obtain a viscous flow activation energy parameter characterizing its temperature-viscosity sensitivity; and, during the reactive melt blending process, based on the viscous flow activation energy parameter, predicting in real time the local temperature rise caused by mechanical shearing, and dynamically adjusting the blending process parameters according to the predicted value of the local temperature rise to prevent premature thermal decomposition of the reactive intumescent flame retardant.

[0012] The second aspect of this application provides an intumescent flame-retardant polyolefin sheathed cable, which is manufactured by any of the methods described above, or has the following structural features.

[0013] An intumescent flame-retardant polyolefin-sheathed cable includes: a conductive core; and a sheath layer covering the conductive core; wherein the sheath layer is composed of a cross-linked flame-retardant polymer composition, the cross-linked flame-retardant polymer composition including a polyolefin matrix and an intumescent flame retardant, wherein the polyolefin matrix molecular chains are covalently connected to each other and to the particles of the intumescent flame retardant, forming a three-dimensional cross-linked network structure with the particles of the intumescent flame retardant as cross-linking hubs.

[0014] Optionally, the sheath layer has an elongation at break greater than 150% and a flame retardant rating of UL94 V-0.

[0015] The beneficial effects of this application are as follows:

[0016] This application proposes a method for constructing an active particle hub-type crosslinking network. By pre-modifying the surface of an intumescent flame retardant, it transforms the inert physical filler into an active center capable of participating in subsequent chemical crosslinking reactions. During reactive extrusion and crosslinking curing, these modified flame retardant particles are no longer free defect points in the polymer matrix, but are firmly embedded in the three-dimensional crosslinking network through covalent bonds, serving as multi-arm crosslinking hubs connecting polymer macromolecular chains. This structural transformation transforms the inorganic particles, originally stress concentration points, into network skeleton nodes capable of effectively transmitting and dispersing stress. Therefore, this application fundamentally solves the inherent contradiction between high-filler-content flame retardants and the mechanical properties of the matrix, significantly improving the elongation at break and toughness of the cable sheath while ensuring a high flame retardant rating, achieving a synergistic gain in flame retardant safety and structural reliability. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating a method for processing an intumescent flame-retardant polyolefin sheathed cable according to one embodiment of this application.

[0019] Figure 2 This is a schematic diagram of the structure of a reactive melt grafting and dispersion module provided in one embodiment of this application.

[0020] Figure 3 This is a schematic diagram of the microstructure of physically blended flame-retardant polyolefins in the prior art.

[0021] Figure 4 This is a schematic diagram of the microstructure of an active particle hub-type crosslinking network constructed in one embodiment of this application.

[0022] Figure 5 This is a schematic diagram of the viscous flow activation energy calibration curve of a polyolefin matrix resin provided in one embodiment of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0025] This application provides a processing method for intumescent flame-retardant polyolefin sheathed cables and the cable products obtained by this method. In a specific implementation, this method employs surface-active modification of the base intumescent flame retardant, followed by reactive melt blending, and finally cross-linking and curing into a network. This enables the construction of a three-dimensional covalent network structure within the polymer matrix, with flame retardant particles serving as cross-linking hubs. This transforms the flame retardant from a destroyer of mechanical properties into an enhancer of the network structure. This method solves the technical problem in existing technologies where the excessive addition of intumescent flame retardants to meet high flame retardancy ratings leads to a sharp decline in key mechanical properties such as the cable sheath's elongation at break, causing potential structural reliability issues. It achieves a high flame retardancy rating of UL94 V-0 while maintaining an elongation at break of over 150%, synergistically improving the cable's safety and durability.

[0026] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0027] Example 1

[0028] Figure 1 This illustration shows a flowchart of a processing method for an intumescent flame-retardant polyolefin-sheathed cable according to one embodiment of this application. This method can be applied to fields such as new energy vehicles, rail transportation, and aerospace, which have high requirements for both flame retardancy and mechanical properties of cables. In a specific application scenario, this method is used to produce high-voltage wiring harnesses for electric vehicles with a rated voltage of 600 / 1000V. These harnesses need to be routed within a confined vehicle space and must withstand long-term vibration, temperature fluctuations, and potential short-circuit thermal shock.

[0029] The method includes the following steps:

[0030] S100: Obtain an active intumescent flame retardant, wherein the active intumescent flame retardant is obtained by surface-active modification of a basic intumescent flame retardant, and the surface of the active intumescent flame retardant is grafted with active functional groups.

[0031] In one specific embodiment, this step is performed in a dedicated surface modification module (M100), which can be a high-speed kneading reactor with high-shear mixing, precise temperature control, and vacuum degassing capabilities. The purpose of this step is to transform the relatively inert basic intumescent flame retardant particles into active functionalized materials capable of actively participating in subsequent polymer grafting and crosslinking reactions, laying the material foundation for the subsequent construction of an active particle-based hub-and-spoke crosslinking network. The core of this step is to anchor a large number of active chemical groups onto the surface of the flame retardant particles through a chemical reaction. These groups act as pre-defined interfaces, enabling them to form stable covalent bonds with the polyolefin matrix macromolecular chains in subsequent processing stages.

[0032] Step S100 can be further broken down into several sub-steps. First, the basic intumescent flame retardant needs to be prepared. In a preferred embodiment, the basic intumescent flame retardant is a classic intumescent flame retardant system composed of an acid source, a char source, and a gas source. Specifically, the acid source can be ammonium polyphosphate (APP), which decomposes upon heating to produce phosphoric acid and polyphosphoric acid, serving as a catalyst and dehydrating agent for the esterification reaction. The char source can be a polyol, for example, pentaerythritol (PER), which contains abundant hydroxyl groups and can be dehydrated and carbonized under the catalysis of phosphoric acid to form a dense foamed char layer framework. The gas source can be melamine (MEL), which decomposes upon heating to release a large amount of non-flammable gas (such as ammonia), causing the molten char layer to foam and expand, forming a porous structure with excellent thermal insulation properties. The synergistic effect of these three components constitutes the basis of the intumescent flame retardant mechanism. In an exemplary formulation, type II APP powder with a degree of polymerization greater than 1000, industrial-grade PER, and MEL powder are weighed in a mass ratio of 3:1:1. Before chemical modification, to ensure highly uniform mixing of the components and increase the surface energy of the particles to improve subsequent reaction efficiency, these three dry powders are placed together in a high-speed mixer and mechanically premixed and activated at 2000 rpm for 30 minutes. This results in a mechanically activated precursor mixture with a more concentrated particle size distribution and increased surface defect sites. This pretreatment facilitates the uniform dispersion and more effective chemical bonding of subsequent modifiers on the particle surface.

[0033] For example, suppose this batch of production requires the preparation of 100 kg of active intumescent flame retardant. Based on a 3:1:1 mass ratio, 60 kg of APP powder, 20 kg of PER powder, and 20 kg of MEL powder need to be weighed. These three powders, totaling 100 kg, are added to a 200-liter high-speed mixer. The mixer is started, the speed is set to 2000 rpm, and the mixing time is 30 minutes. During this process, the strong mechanical shear force not only breaks down and redistributes the particles of different components but may also generate tiny cracks and active sites on the particle surface, providing more reaction possibilities for subsequent chemical grafting reactions. After mixing, 100 kg of a homogeneous basic intumescent flame retardant mixture is obtained, with an average particle size (D50) measured by a laser particle size analyzer and controlled to be approximately 15 micrometers.

[0034] Next, a surface-active modification treatment is performed on the base intumescent flame retardant. The core of this treatment is the introduction of a bridging molecule, a coupling agent, which has one end capable of binding to the surface of the inorganic flame retardant particles and the other end containing an active functional group capable of reacting with the organic polymer matrix. In a preferred embodiment, a silane coupling agent is used to perform this task. The silane coupling agent's molecular structure contains at least one hydrolyzable group (such as methoxy or ethoxy), which can undergo a condensation reaction with a small number of hydroxyl or polar groups present on the surface of the base intumescent flame retardant particles (especially APP) to form a stable chemical bond (Si-OP or Si-OC); simultaneously, the silane coupling agent molecule also contains at least one non-hydrolyzable organic functional group, i.e., the active functional group. To enable this active functional group to participate in subsequent free radical-initiated graft polymerization and crosslinking reactions, preferably, the active functional group is an unsaturated double bond, such as a vinyl group. Therefore, a particularly preferred silane coupling agent is vinyltrimethoxysilane (VTMO) or vinyltriethoxysilane (VTEO).

[0035] The specific modification procedure is as follows: 100 kg of the base intumescent flame retardant mixture obtained in the previous step is transferred to a heatable kneading reactor and stirred at a low speed (e.g., 60 rpm). Simultaneously, the reactor is heated to 100°C and evacuated to -0.08 MPa to preheat the material and remove any adsorbed trace amounts of moisture. Then, the modifier solution is slowly and evenly sprayed into the stirred powder through an atomizing nozzle. The modifier solution is pre-prepared, for example, by dissolving 2 kg (2 wt% of the total flame retardant weight) of VTMO and 0.1 kg (0.1 wt% of the total flame retardant weight) of the initiator dicumyl peroxide (DCP) in 10 liters of anhydrous ethanol. The addition of DCP is intended to slightly initiate the reaction between VTMO and the particle surface. The spraying process lasts approximately 20 minutes to ensure sufficient contact between the solution and each powder particle. After spraying, the temperature of the reactor is raised to 110 degrees Celsius and maintained at this temperature for 2 hours. During this period, the methoxy groups in the VTMO molecules undergo hydrolysis under the influence of trace amounts of moisture and heat, generating active silanol groups (-Si-OH). These silanol groups then undergo a de-alcoholization condensation reaction with hydroxyl groups or polar sites on the surface of APP particles to form chemical bonds, thereby firmly grafting vinyl-containing siloxane fragments onto the surface of the flame retardant particles. After the reaction is complete, stirring is continued at 110 degrees Celsius under vacuum for 30 minutes to completely remove the reaction byproduct methanol and the ethanol used as a solvent. Finally, the material is cooled and discharged to obtain approximately 101.5 kg (considering the grafted organic matter), a free-flowing white powder with a large number of active vinyl functional groups grafted onto its surface, which is the active intumescent flame retardant (A-IFR).

[0036] S200: The active intumescent flame retardant, a polyolefin matrix resin, and an initiator are reactively melt-blended to obtain a crosslinkable flame-retardant polyolefin composition.

[0037] Step S200 is crucial for achieving chemical bonding between the flame retardant and the polymer matrix, and for preparing a prepolymer with the final cross-linking and curing capability. This step is carried out in a reactive extrusion system (M200) specifically designed for high-filler, high-viscosity materials, typically using a co-rotating parallel twin-screw extruder due to its excellent self-dispersing, self-cleaning, and heat exchange capabilities. Figure 2 As shown, an exemplary twin-screw extruder 200 has multiple temperature zones (201-206), a main feed port 210, a side feed port 220, and a vacuum vent 230. The reactivity of this step is reflected in the fact that, simultaneously with melting and physical mixing, a chemical grafting reaction triggered by an initiator occurs within the system.

[0038] First, the polyolefin matrix resin is selected. To balance the material's flexibility, processability, and compatibility with flame retardants, a composite resin system is chosen in this embodiment. Specifically, ethylene-vinyl acetate copolymer (EVA) and low-density polyethylene (LDPE) are premixed at a mass ratio of 3:1. EVA, due to the presence of polar vinyl acetate groups in its molecular chain, exhibits good initial physical compatibility with the semi-polar IFR system while also providing excellent flexibility. LDPE helps regulate the system's melt strength and processing fluidity. In a specific formulation, the polyolefin matrix resin accounts for 70 wt% of the total mass of the final cable sheath, while the active intumescent flame retardant A-IFR obtained in step S100 accounts for 30 wt%. Therefore, for a 100 kg production batch, 52.5 kg of EVA resin (exemplarily, a grade with VA content of 28%) and 17.5 kg of LDPE resin (exemplarily, a grade with a melt index of 2.0 g / 10 min) need to be prepared.

[0039] Next, the initiator is selected. The initiator's role is to generate active free radicals through thermal decomposition during reactive extrusion. These free radicals abstract hydrogen atoms from the polyolefin macromolecular chain (especially tertiary carbon atoms), forming macromolecular free radicals. These macromolecular free radicals then attack the vinyl double bonds on the surface of the A-IFR particles, undergoing an addition reaction, thereby achieving the purpose of grafting A-IFR particles onto the polyolefin macromolecular chain. In this embodiment, dicumyl peroxide (DCP) is selected as the initiator, as its decomposition temperature matches the processing temperature window of the polyolefin well. The amount of initiator needs to be precisely controlled; too little will result in low grafting efficiency, while too much may cause excessive cross-linking of the polymer in the extruder, leading to gelation and making it unprocessable. For example, the amount of DCP added is 0.5 wt% of the main resin mass, i.e., (52.5 + 17.5) 0.5% = 0.35 kg.

[0040] The specific reactive melt blending operation is as follows: The temperatures of each zone of the twin-screw extruder 200 are set, for example, from the feeding section to the die section, sequentially set to 120℃, 145℃, 155℃, 160℃, 165℃, and 160℃. The main unit is started, and the screw speed is set to 250 rpm. The premixed EVA / LDPE resin particles (total 70 kg) are added to the extruder at a constant rate through the loss-in-weight feeder at the main feed port 210. The resin particles are conveyed and completely melted by the screw in the first and second temperature zones (201, 202) to form a continuous polymer melt. In the third temperature zone (203), 30 kg of A-IFR powder obtained in step S100 and 0.35 kg of DCP (premixed with a small amount of A-IFR to ensure uniform dispersion) are forcibly fed into the polymer melt in a precise ratio through another loss-in-weight feeder at the side feed port 220. After A-IFR and DCP enter, they undergo intense distribution and dispersion mixing with the polymer melt in the high-shear mixing section (fourth and fifth temperature zones 204 and 205) composed of multiple sets of meshing discs and kneading blocks. Under this high temperature and strong shear, DCP decomposes to generate active free radicals, initiating a grafting reaction of A-IFR onto the polyolefin matrix. Simultaneously, a vacuum exhaust port 230 located at the rear of the fifth temperature zone promptly removes any small amount of volatile byproducts that may be generated during the reaction. After thorough mixing and reaction, the material is finally extruded from the die to form strips. After passing through a cooling water tank and a pelletizer, uniform, non-porous granular products are obtained, namely the crosslinkable flame-retardant polyolefin composition. The composition is characterized by the fact that the A-IFR particles are already chemically bonded to some of the polyolefin macromolecular chains, and the entire system retains a large number of unreacted silane groups introduced by VTMO, preparing for the final crosslinking and curing step.

[0041] S300: The crosslinkable flame-retardant polyolefin composition is coated onto the outer surface of a conductive wire core to form a sheath layer.

[0042] Step S300 is the cable forming process, which is typically completed on a single-screw extrusion coating production line. This production line includes a pay-off frame, conductor preheating device, single-screw extruder, cross-cut die, cooling water tank, traction device, and take-up reel, etc.

[0043] In one specific embodiment, the conductive core is a bundle of conductors with a cross-sectional area of ​​10 square millimeters, formed by strands of tinned copper wire. After being released from the pay-off stand, the conductive core first passes through a preheating device, heating it to approximately 80°C to remove surface moisture and improve adhesion to the subsequent molten sheath layer. Simultaneously, the crosslinkable flame-retardant polyolefin composition particles obtained in step S200 are added to the hopper of a single-screw extruder. The temperature of the single-screw extruder is set to 160°C, and the screw speed is adjusted to match the core traction speed to ensure stable extrusion volume. The molten composition is coaxially and uniformly coated onto the conductive core passing through the center of the die using a cross-shaped extrusion die. The dimensions of the die orifice and core die are precisely designed to ensure uniform sheath layer thickness after extrusion, for example, controlled at 1.0 mm. After leaving the die, the sheathed cable semi-finished product immediately enters a cooling and setting water tank for rapid cooling and solidification, forming a dimensionally stable sheath layer.

[0044] For example, the traction speed of the conductive core is set to 20 meters per minute. Based on this linear speed and the required sheath size, the control system calculates the theoretical extrusion volume required by the single-screw extruder using a preset mathematical model and automatically adjusts the screw speed to match this extrusion volume. For instance, if the calculation shows that 0.8 kg of melt needs to be extruded per minute, the screw speed is set to 80 revolutions per minute. The outer diameter of the sheath is monitored in real time using an online laser diameter gauge, and the data is fed back to the control system, forming a closed-loop control to ensure the long-term stability of the sheath thickness, with fluctuations controlled within ±0.05 mm. After this step, we obtain a semi-finished cable with an uncrosslinked or semi-crosslinked sheath. At this point, the sheath has a basic shape and a certain strength, but its internal chemical crosslinking network is not yet fully formed, and its mechanical properties and heat resistance do not meet the final requirements.

[0045] S400: The sheath layer is subjected to cross-linking and curing treatment to form a three-dimensional cross-linked network structure within the sheath layer, wherein the particles of the active intumescent flame retardant serve as cross-linking hubs in the three-dimensional cross-linked network structure.

[0046] Step S400 is the final and most crucial step in the method of this invention to achieve a qualitative change in the performance of the sheath material. Through this step, the chemical potential embedded in the system in step S200 is fully activated, constructing the final, highly stable active particle hub-type cross-linked network.

[0047] In a preferred embodiment, a warm water crosslinking and curing process is employed. This method utilizes the penetration of water molecules to trigger hydrolysis and condensation reactions of the silane groups introduced by VTMO in the system. Specifically, the semi-finished cable produced in step S300 is coiled onto a take-up reel, and then the entire reel is immersed in a large hot water bath maintained at a constant temperature of 90±2°C. High-temperature water molecules act as reactants, slowly penetrating into the interior of the polyolefin sheath. When water molecules encounter VTMO residues (-Si-(OCH3)3) grafted onto the polyolefin chain or the surface of A-IFR particles, they undergo hydrolysis to generate active silanol groups (-Si-(OH)3). These highly reactive silanol groups rapidly undergo dehydration condensation reactions with neighboring silanol groups, forming very stable siloxane bonds (-Si-O-Si-). Since each VTMO residue can generate three silanol groups, this condensation reaction takes place in three-dimensional space, thereby completely stitching together different polyolefin macromolecular chains and A-IFR particles linked by the macromolecular chains through strong siloxane chemical bonds.

[0048] This process continues, ultimately forming a dense and robust three-dimensional covalently cross-linked network within the entire volume of the sheath material. This network is characterized by A-IFR particles as core nodes, polyolefin macromolecular chains as connecting arms, and siloxane bonds as interlocking links. For example... Figure 4 The microstructure shown 400, the active intumescent flame retardant particles 410 are no longer like Figure 3 Instead of existing as a free entity like in (310), it is tightly connected to the polyolefin matrix 420 through covalent bonds 430, becoming part of the network. This structure fundamentally eliminates the interfacial weakness between the inorganic filler and the organic matrix, allowing stress to be effectively transferred and dispersed in the network, rather than accumulating at the interface and causing cracks. The crosslinking time depends on the thickness of the sheath. For a 1.0 mm thick sheath layer, it is usually necessary to soak and treat it in hot water at 90°C for 2 hours to ensure that the crosslinking reaction is fully carried out, and the gel rate (an indicator of the degree of crosslinking) can reach more than 75%. After crosslinking is completed, the coil is removed, cooled and dried to obtain the final product, the intumescent flame-retardant polyolefin sheathed cable.

[0049] Optionally, in applications with extremely high production efficiency requirements, the crosslinking curing process can also be performed using irradiation crosslinking. In this case, the formulation needs to be slightly adjusted, for example, by adding a small amount of multifunctional crosslinking agent (such as trimethylolpropane trimethacrylate, TMPTMA) in step S200. The extruded and coated semi-finished cable is passed directly under an electron beam accelerator. The high-energy electron beam (e.g., 1.5-2.5 MeV) penetrates the sheath layer, breaking the CH bonds on the polymer chains and generating a large number of macromolecular free radicals. These free radicals rapidly combine with each other or react with the crosslinking agent and the vinyl groups on the A-IFR surface, completing the construction of a three-dimensional crosslinked network instantaneously (on the order of seconds). The advantages of irradiation crosslinking are its extremely high speed and lack of water treatment requirements, but the equipment investment is relatively high.

[0050] Example 2

[0051] This embodiment provides an online quality control method involved in the processing system of intumescent flame-retardant polyolefin sheathed cables. This method is a deepening and refinement of step S200 in Embodiment 1.

[0052] In the S200 reactive melt blending process of Example 1, a key technical challenge is preventing the intumescent flame retardant from prematurely foaming within the extruder. The foaming initiation temperature of the IFR system is typically around 175°C. However, under high speed and high filler conditions, the local instantaneous temperature of a twin-screw extruder may be much higher than the barrel's set temperature due to viscous dissipation within the melt (i.e., mechanical energy converted into heat). Once the local temperature becomes uncontrolled, the gas generated by the flame retardant foaming will result in a large number of pores within the extruded material, directly causing product spoilage. Furthermore, different batches of polyolefin raw materials exhibit slight differences in rheological properties such as viscosity and molecular weight distribution, leading to variations in their shear heating behavior under the same processing parameters. Therefore, this example provides a feedforward-feedback intelligent temperature control method based on rheological property calibration.

[0053] This method adds an S000 system initialization and shear rheological base calibration step before the formal start of step S200.

[0054] S000: The rheological properties of the polyolefin matrix resin are calibrated to obtain the viscous flow activation energy parameter characterizing its temperature-viscosity sensitivity. Specifically, before production begins, a small amount (e.g., 5 kg) of the current batch of EVA / LDPE mixed resin is added to the twin-screw extruder through the main feed port. Then, a preset automated calibration program is executed. This program controls the extruder at a low speed (e.g., 100 rpm to reduce interference from shear heating) and sequentially sets the barrel temperature at several different levels, such as 140°C, 150°C, and 160°C. After each temperature point stabilizes, the system records the torque value required to drive the screw rotation. Since the torque is proportional to the apparent viscosity of the melt within the screw, a set of temperature-viscosity correlation data points can be obtained.

[0055] An Arrhenius rheological calibration model is embedded within the control system. This model is based on a well-known physical principle: the apparent viscosity of polymer melts. With absolute temperature The relationship between them, within a certain temperature range, can be described by the Arrhenius equation: .in, It is a forward factor. It is the ideal gas constant, while This refers to the activation energy of viscous flow, which characterizes the sensitivity of viscosity to temperature changes. The larger the value, the more sensitive the viscosity is to temperature changes. For ease of calculation, this equation can be transformed into a logarithmic linearization: This is shaped like... The linear equation.

[0056] For example, suppose the calibration procedure measures the following data: At that time, apparent viscosity after torque conversion ;exist hour, ;exist hour, The system will store these data points ( Perform linear regression fitting to obtain the slope of a straight line. For example, calculate the slope. According to the relation The viscous flow activation energy of the current batch of resin can be calculated immediately. .this The value is then stored in the control system's database as a rheological fingerprint for the current production batch.

[0057] During the formal production of S200 reactive melt blends, the system will continuously perform dynamic control. An internal viscous dissipation temperature rise prediction model is also implemented in the control system. This model, based on fluid dynamics principles, is used to estimate the local temperature rise caused by mechanical shearing. Its core governing equation is: .in, This is the temperature measured by the current temperature sensor. This is the predicted local maximum temperature of the melt. (The formula contains...) This refers to apparent viscosity, which is no longer a fixed value but is determined by the Arrhenius equation based on the current measured temperature. And the one that was just marked It is calculated in real time. It is the instantaneous shear rate related to the current screw speed and screw geometry. It is the residence time of the melt in the high-shear region. and These are the density and specific heat capacity of the melt, respectively, which can be used as preset constants.

[0058] For example, when the extruder is running at a high speed of 300 rpm, the system monitors the actual temperature of the fifth temperature zone as 165°C (438.15 K). The control system immediately invokes the Arrhenius model to calculate the apparent viscosity of the current batch of resin at that temperature. Approximately Simultaneously, based on a rotation speed of 300 rpm, the system calculates the highest shear rate in the kneading block region. Reached Assume the residence time of the material in this area. The melting time is 1.8 seconds, and the melt density is... for Specific heat capacity for The system substitutes these parameters into the temperature rise prediction equation to calculate the local temperature rise. Although this calculation result is a theoretical maximum value based on an adiabatic model, after correction by an empirical factor (e.g., 0.1), the actual predicted temperature rise is approximately 35.2 K (i.e., 35.2 °C). Therefore, the predicted local maximum temperature of the melt is... This predicted value far exceeds the foaming critical point of 175℃. Therefore, the control system immediately triggers a protection mechanism the instant the calculation is completed (in milliseconds), automatically limiting the screw speed to 260 rpm or increasing the water flow rate of the fifth temperature zone cooling system, thereby keeping the actual local peak temperature below the safe threshold. Through this intelligent feedforward-feedback control, the stability and yield of the high-filler flame-retardant material production process are greatly improved.

[0059] Example 3

[0060] This embodiment provides an expansion-retardant polyolefin sheathed cable product according to the above description.

[0061] This cable product comprises a conductive core and an outer sheath. The conductive core can be composed of single or multiple strands of copper or aluminum conductor, and its cross-sectional area is determined according to the cable's rated current carrying capacity. The sheath is the core innovation of this cable product, and it is composed of a special cross-linked flame-retardant polymer composition.

[0062] From a macroscopic perspective, the sheath layer exhibits a uniform, dense, and smooth surface. The color can be adjusted by adding color masterbatch as needed. It has a uniform thickness and excellent abrasion resistance and chemical resistance.

[0063] From a microstructural perspective, the sheath layer exhibits a unique Active Particulate Hub-Type Crosslinked Network (APHCN). This network comprises two main components: a polyolefin matrix as the continuous phase and intumescent flame retardant particles as the dispersed phase, deeply involved in network construction. Unlike the island-like structures in existing technologies where flame retardant particles act merely as physical fillers, relying solely on van der Waals forces or a small amount of compatibilizer for interaction with the matrix, the sheath layer in this application connects the macromolecular chains of the polyolefin matrix, as well as the surfaces of the polyolefin macromolecular chains and the intumescent flame retardant particles, through stable covalent chemical bonds. This makes each flame retardant particle act as a hub or node, firmly anchoring several surrounding polymer chains together. This structure makes the entire sheath material a complete and unified chemical whole, fundamentally eliminating the weak interface between the inorganic filler and the organic matrix.

[0064] Due to this unique microstructure, the cable sheath layer exhibits synergistically enhanced macroscopic properties.

[0065] On the one hand, it exhibits excellent flame-retardant properties. When the cable encounters high-temperature conditions such as fire, the intumescent flame retardant (APP / PER / MEL) can still effectively expand and char, rapidly forming a thick, dense, and porous char layer on the cable surface. This char layer effectively insulates against heat transfer to the internal polymer and prevents oxygen from entering, thereby inhibiting combustion. Because the flame retardant is uniformly chemically bonded within the network, it avoids the agglomeration or migration phenomena that may occur in traditional technologies, resulting in a higher quality and more uniform char layer, and a correspondingly improved flame-retardant efficiency. Standard testing shows that the flame-retardant rating of this sheath layer consistently reaches the highest level, V-0, in the UL94 standard.

[0066] On the other hand, its mechanical properties, especially flexibility and tensile strength, have been revolutionaryly improved. In traditional physical blending systems, when the cable is stretched or bent, stress concentrates at the interface between the rigid flame retardant particles and the flexible polymer matrix. Due to the weak interfacial bonding, tiny cracks initiate and rapidly propagate at this point, leading to brittle fracture of the material under very small deformation. However, in the APHCN structure of this application, when the material is under stress, the stress can be smoothly transferred from the flexible polymer chains to the rigid flame retardant particle hubs through strong covalent bonds, and then dispersed throughout the entire three-dimensional network by these robust nodes. The flame retardant particles are no longer weak points, but rather become the skeleton that strengthens the entire network structure. Therefore, this sheath layer can withstand greater deformation without breaking. Tensile performance tests conducted according to GB / T 2951.11 standard show that the elongation at break of this sheath layer can consistently reach over 150%, and in some optimized formulations, it can even exceed 200%, while the elongation at break of traditional materials with the same amount of flame retardant is usually less than 100%. This high flexibility makes cable installation in confined spaces easier and significantly improves its resistance to fatigue and cracking under long-term vibration, greatly enhancing the overall reliability and service life of the cable.

[0067] In summary, the cable product provided in this application, through its unique internal chemical microstructure, successfully unifies the two long-standing mutually restrictive performance indicators of flame retardancy safety and mechanical reliability to a higher level of synergistic enhancement, thus meeting the stringent requirements of the next generation of high-performance cables.

[0068] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0069] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit described above can be implemented in hardware.

[0070] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for processing an intumescent flame-retardant polyolefin sheathed cable, characterized in that, include: An active intumescent flame retardant is obtained by surface-active modification of a basic intumescent flame retardant, wherein the surface of the active intumescent flame retardant is grafted with active functional groups. The active intumescent flame retardant, a polyolefin matrix resin, and an initiator are reactively melt-blended to obtain a crosslinkable flame-retardant polyolefin composition. The crosslinkable flame-retardant polyolefin composition is coated onto the outer surface of a conductive wire core to form a sheath layer; and The sheath layer is subjected to cross-linking and curing treatment to form a three-dimensional cross-linked network structure within the sheath layer, wherein the particles of the active intumescent flame retardant serve as cross-linking hubs in the three-dimensional cross-linked network structure.

2. The method according to claim 1, characterized in that, The basic intumescent flame retardant includes ammonium polyphosphate, a polyol carbon source, and a gas source.

3. The method according to claim 2, characterized in that, The polyol carbon source is pentaerythritol, and the gas source is melamine.

4. The method according to claim 1, characterized in that, The surface-active modification treatment includes: reacting the base intumescent flame retardant with a silane coupling agent to graft the active functional group onto the surface of the base intumescent flame retardant; wherein the silane coupling agent contains at least one functional group that can react with the surface groups of the base intumescent flame retardant, as well as the active functional group.

5. The method according to claim 4, characterized in that, The active functional group is vinyl, and the silane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane.

6. The method according to claim 1, characterized in that, The polyolefin matrix resin includes at least one of ethylene-vinyl acetate copolymer and low-density polyethylene.

7. The method according to claim 1, characterized in that, The cross-linking curing treatment includes warm water cross-linking curing treatment or irradiation cross-linking curing treatment.

8. The method according to claim 1, characterized in that, Prior to the reactive melt blending, the following is also included: The rheological properties of the polyolefin matrix resin were calibrated to obtain the viscous flow activation energy parameter characterizing its temperature-viscosity sensitivity. Furthermore, during the reactive melt blending process, the local temperature rise caused by mechanical shearing is predicted in real time based on the viscous flow activation energy parameter, and the blending process parameters are dynamically adjusted according to the predicted value of the local temperature rise to prevent the active intumescent flame retardant from undergoing premature thermal decomposition.

9. An intumescent flame-retardant polyolefin sheathed cable, characterized in that, include: One conductive wire core; as well as A sheath layer covering the conductive wire core; The sheath layer is composed of a cross-linked flame retardant polymer composition, which includes a polyolefin matrix and an intumescent flame retardant. The polyolefin matrix molecular chains are connected to each other and to the particles of the intumescent flame retardant by covalent bonds, forming a three-dimensional cross-linked network structure with the particles of the intumescent flame retardant as the cross-linking hub.

10. The cable according to claim 9, characterized in that, The sheath layer has an elongation at break of more than 150% and its flame retardant rating reaches UL94 V-0.

Images