Halogen-free low-smoke flame-retardant polyolefin cable

Abstract

The invention discloses a halogen-free low-smoke flame-retardant polyolefin cable which comprises a composite cable core, a first flame-retardant wrapping tape layer, an inner sheath, a second flame-retardant wrapping tape layer, a waterproof layer, a metal sheath layer and an outer sheath which are sequentially arranged from inside to outside. The outer sheath is made of a ceramic polyolefin material which is extruded and covered on the metal sheath layer. According to the low-smoke halogen-free cable, the ceramic polyolefin outer sheath is introduced into the cable structure, so that the problems of sheath softening, insulating layer stripping, structure collapse and the like of a traditional low-smoke halogen-free cable during high-temperature combustion are effectively solved. The ceramic polyolefin material can be converted into a compact ceramic layer under the action of flame to form a firm heat insulation barrier, so that the integral structure of the cable is kept complete, flame spreading and conductor short circuit are prevented, and the fire resistance and continuous power supply performance are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of wire and cable technology, and in particular to a halogen-free, low-smoke, flame-retardant polyolefin cable. Background Technology

[0002] With rapid economic development and accelerated urbanization, the application scope of power systems and electrical equipment is constantly expanding. As a crucial carrier of electrical energy and signal transmission, the safety and reliability of cables have become a key consideration in engineering construction. Especially in densely populated or high-risk environments such as subways, high-rise buildings, hospitals, and public places, the toxic fumes, corrosive gases, and flame spread rate generated when cables burn directly affect personnel evacuation and property safety. Therefore, higher requirements are placed on the flame-retardant, low-smoke, and halogen-free properties of cables.

[0003] While traditional polyvinyl chloride (PVC) insulated cables possess some flame-retardant properties, they release large amounts of hydrogen chloride gas and black smoke when burning. This not only affects visibility and escape time but also causes severe corrosion to electronic equipment and metal components, making them unsuitable for modern high-safety-standard applications. To improve environmental safety, low-smoke halogen-free flame-retardant polyolefin (LSZH) materials are gradually replacing traditional PVC materials, becoming the main development direction. However, existing low-smoke halogen-free flame-retardant cables may still experience insulation peeling and outer sheath cracking during high-temperature combustion, leading to conductor short circuits or failure, thus affecting the system's continuous power supply capability.

[0004] Therefore, how to further improve the structural integrity and heat insulation of cables under combustion conditions while ensuring low smoke and halogen-free properties has become a hot research topic in the field of flame-retardant cable technology. Summary of the Invention

[0005] To address the technical problems in the prior art where existing low-smoke halogen-free flame-retardant cables may still experience insulation peeling and outer sheath cracking during high-temperature combustion, the present invention aims to provide a halogen-free, low-smoke flame-retardant polyolefin cable.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] This invention provides a halogen-free, low-smoke flame-retardant polyolefin cable, comprising a composite cable core, a first flame-retardant wrapping tape layer, an inner sheath, a second flame-retardant wrapping tape layer, a water-blocking layer, a metal sheath layer, and an outer sheath arranged sequentially from the inside out.

[0008] The outer sheath is made of ceramicized polyolefin material extruded and covered on a metal sheath layer.

[0009] In a preferred embodiment, the ceramicized polyolefin material comprises the following components in parts by weight:

[0010]

[0011]

[0012] In a preferred embodiment, the composite flame retardant A is an intumescent flame retardant composite, which comprises iron oxide, zinc borate, sepiolite and modified ammonium polyphosphate.

[0013] In a preferred embodiment, the preparation method of the modified ammonium polyphosphate is as follows:

[0014] The ammonium polyphosphate is dispersed in a mixture of anhydrous ethanol and deionized water, the mass ratio of anhydrous ethanol and deionized water is 2:1, and 20g of ammonium polyphosphate is added per 100ml of mixed solution;

[0015] Ammonia water is added to adjust the PH of the mixed solution to 10;

[0016] Phenyltrimethoxysilane and tetraethyl orthosilicate are added to the mixed solution, and the mixed solution is stirred uniformly with a glass cup, the mass ratio of the ammonium polyphosphate, phenyltrimethoxysilane and tetraethyl orthosilicate is 5:1:1;

[0017] The mixed solution is stirred and reacted at 40℃ for 3h, and then filtered and washed with anhydrous ethanol;

[0018] The washed powder is placed in a Soxhlet extractor and extracted with anhydrous ethanol for 24h, and then dried in an electric heating air drying oven to obtain the modified ammonium polyphosphate powder.

[0019] In a preferred embodiment, the inner sheath is covered on the first flame-retardant wrapping tape layer by extruding a ceramicized silicone rubber material.

[0020] In a preferred embodiment, the ceramicized silicone rubber material comprises the following components by weight:

[0021]

[0022] In a preferred embodiment, the composite flame retardant B is a mixture of inorganic hydroxide, antimony trioxide and magnesium aluminum carbonate hydrotalcite, and the mass ratio of inorganic hydroxide, antimony trioxide and magnesium aluminum carbonate hydrotalcite is 5:1:3.

[0023] In a preferred embodiment, the composite cable core comprises a plurality of insulated wire cores, each insulated wire core comprising a conductor and an insulating layer wrapped around the outer surface of the conductor;

[0024] The insulating layer is a polyvinyl chloride sheath material extruded on the conductor.

[0025] In a preferred embodiment, an oxygen-barrier filler is used between the composite cable core and the first flame-retardant wrapping tape layer. The oxygen-barrier filler is fireproof putty that is semi-extruded onto the composite cable core.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] This invention provides a halogen-free, low-smoke flame-retardant polyolefin cable, comprising, from the inside out, a composite cable core, a first flame-retardant wrapping tape layer, an inner sheath, a second flame-retardant wrapping tape layer, a water-blocking layer, a metal sheath layer, and an outer sheath. The outer sheath is made of ceramicized polyolefin material extruded and covering the metal sheath layer.

[0028] This invention effectively solves the problems of sheath softening, insulation peeling, and structural collapse that often occur in traditional low-smoke halogen-free cables during high-temperature combustion by introducing a ceramicized polyolefin outer sheath into the cable structure. Under flame conditions, the ceramicized polyolefin material transforms into a dense ceramic layer, forming a robust heat insulation barrier, maintaining the integrity of the overall cable structure, preventing flame spread and conductor short circuits, and significantly improving fire resistance and continuous power supply performance. Simultaneously, combined with a composite protective design of multi-layer flame-retardant wrapping tape, a water-blocking layer, and a metal sheath, this cable system maintains low-smoke, halogen-free, and environmentally friendly characteristics while also possessing excellent heat insulation, waterproofing, and mechanical protection capabilities. It meets the application requirements of high-safety locations such as subways, high-rise buildings, and hospitals. Overall, this invention balances flame retardancy, structural stability, and environmental safety, significantly improving the reliability and service life of cables in extreme environments. Attached Figure Description

[0029] Figure 1 This is a cable structure diagram of a halogen-free, low-smoke, flame-retardant polyolefin cable according to the present invention.

[0030] In the picture:

[0031] 100 - Conductor;

[0032] 200 - Insulation layer;

[0033] 300 - First flame-retardant wrapping tape layer;

[0034] 400 - Inner sheath;

[0035] 500 - Second flame-retardant wrapping tape layer;

[0036] 600 - Water-blocking layer;

[0037] 700 - Metal sheath layer;

[0038] 800 - Outer sheath. Detailed Implementation

[0039] To facilitate understanding of the present invention, the technical solutions and advantages of the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Any mechanisms or methods not elaborated in this invention can be referred to in the prior art. The specific structures and features of the present invention are illustrated below by way of example and should not be construed as limiting the present invention in any way. Furthermore, any of the technical features mentioned below (including implicit or disclosed features), as well as any technical features directly shown or implied in the figures, can be arbitrarily combined or deleted among these technical features to form more other embodiments that may not be directly or indirectly mentioned in this invention. The accompanying drawings show preferred embodiments of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0040] While traditional polyvinyl chloride (PVC) insulated cables possess some flame-retardant properties, they release large amounts of hydrogen chloride gas and black smoke when burning. This not only affects visibility and escape time but also causes severe corrosion to electronic equipment and metal components, making them unsuitable for modern high-safety-standard applications. To improve environmental safety, low-smoke halogen-free flame-retardant polyolefin (LSZH) materials are gradually replacing traditional PVC materials, becoming the main development direction. However, existing low-smoke halogen-free flame-retardant cables may still experience insulation peeling and outer sheath cracking during high-temperature combustion, leading to conductor short circuits or failure, thus affecting the system's continuous power supply capability.

[0041] Therefore, the present invention provides a halogen-free, low-smoke flame-retardant polyolefin cable, such as... Figure 1 As shown, this invention presents a preferred structure for a flame-retardant polyolefin cable.

[0042] like Figure 1 As shown, the halogen-free, low-smoke, flame-retardant polyolefin cable of the present invention comprises, from the inside out, a composite cable core, a first flame-retardant wrapping tape layer 300, an inner sheath 400, a second flame-retardant wrapping tape layer 500, a water-blocking layer 600, a metal sheath layer 700, and an outer sheath 800. The outer sheath 800 is a ceramicized polyolefin material extruded and covering the metal sheath layer.

[0043] The main innovations of this invention are as follows:

[0044] (1) Balancing flame retardancy and structural integrity:

[0045] The outer sheath of this invention is made of ceramicized polyolefin material, which undergoes physical phase change and chemical reaction during high-temperature combustion to form a dense ceramic layer structure. This ceramic layer can maintain the cable's shape and structure integrity in flames, preventing the internal insulation layer from being exposed or short-circuited due to sheath softening, melting, or detachment, thus significantly improving the cable's fire-resistant and continuous power supply capability.

[0046] (2) Low smoke and halogen-free, environmentally friendly and safe:

[0047] The polyolefin matrix of ceramicized polyolefin materials is halogen-free, and does not release toxic and corrosive gases such as hydrogen halides during combustion. It has low smoke density and low toxicity, which can effectively reduce harmful smoke and corrosive environment at the fire scene, extend the evacuation time of personnel, and protect electronic equipment and building structures, meeting the high safety and environmental protection requirements of modern buildings and public facilities.

[0048] (3) Excellent synergistic effect of heat insulation and flame retardancy:

[0049] The outer sheath, made of ceramicized polyolefin material, forms a multi-level protective structure with the cable's internal structure. The outer ceramic layer effectively blocks external heat transfer, while the inner flame-retardant wrapping layer further suppresses flame spread, achieving excellent synergistic effects of heat insulation and flame retardancy. This structure significantly delays conductor temperature rise and maintains stable insulation performance. Furthermore, through this multi-layered composite structure design, the cable of this invention maintains stable mechanical strength and electrical performance under conditions such as fire, humidity, and high temperature, reducing the risk of system interruption caused by sheath rupture, insulation stripping, or short circuits. This significantly improves the safety and reliability of the power system and extends the cable's service life.

[0050] In a preferred embodiment, the ceramicized polyolefin material comprises the following components in parts by weight:

[0051]

[0052] In this application, EVA and POE provide matrix toughness and flexibility, ensuring good ductility and strain resistance during extrusion processing and service. LLDPE enhances the mechanical strength and weather resistance of the outer sheath. Wollastonite fibers and glass powder form an inorganic skeleton during high-temperature combustion, promoting ceramicization of the material surface. Composite flame retardant A provides the main flame retardant and ceramicization functions. Antioxidants (type 1010 or 168) prevent the polymer from thermal-oxidative aging during processing and use. Lubricants (stearates) improve extrusion flowability and interfacial compatibility.

[0053] In one specific embodiment, the modified nano-ceramic is prepared by the following method:

[0054] (1) Raw material mixing: Nano-clay is mixed with aminopropyltriethoxysilane to obtain a mixture; wherein, the amount of aminopropyltriethoxysilane is 3-5% of the mass of nano-clay;

[0055] (2) Heating and stirring: Heat the mixture to 50-60°C and stir continuously for 20-30 minutes;

[0056] (3) Add nano silica: Add 1.5% of the total mass of nano silica to the heated and stirred mixture;

[0057] (4) High-speed dispersion: The mixture with added nano-silica is subjected to high-speed dispersion treatment to obtain modified nano-ceramic.

[0058] In this invention, modified nano-ceramic clay, due to its nanoscale dispersion and surface modification, can significantly improve the hardness, strength, and toughness of the material. The performance of the nano-ceramic composite material at high temperatures is improved, including increased hardness and strength. Pressure resistance and impact resistance: Modified nano-ceramic clay enhances the material's barrier and airtightness, exhibiting good pressure resistance and impact resistance. Heat sealing performance: It features high heat sealing strength and good heat sealing performance.

[0059] This application employs a synergistic effect of modified nano-ceramic clay and wollastonite mineral fibers, resulting in a significant "microscopic filling + interfacial adhesion enhancement + sintering assistance" effect within the ceramicized polyolefin sheath system. In the ceramicized polyolefin sheath material of this invention, wollastonite mineral fibers primarily serve as a macroscopic skeletal filler. Their fibrous structure maintains its overall morphology at high temperatures, providing a continuous support network for the ceramicized layer and preventing the material from melting, dripping, or collapsing under combustion or high-temperature conditions, thereby enhancing the mechanical stability of the ceramic layer. Meanwhile, the modified nano-ceramic clay, in the form of nano-sized particles, is uniformly dispersed between the polyolefin matrix and the wollastonite mineral fibers, achieving good interfacial bonding with the polyolefin and graft compatibility agent through surface modification.

[0060] During the ceramization process, nano-ceramic clay fills the gaps between fibers and micropores, promoting the sintering of glass powder and low-melting-point flux, thereby forming a dense ceramic network structure. The combination of wollastonite mineral fibers and modified nano-ceramic clay forms a multi-level network structure of macro-skeleton + micro-filling, achieving a synergistic effect of physical support and interfacial adhesion enhancement. This structure can significantly improve the tensile strength, hardness, and toughness of the sheath material, while also improving its compressive strength and impact resistance. In addition, the synergistic network hinders heat conduction and flame propagation at high temperatures, improving the material's flame retardancy and fire resistance limit. The micro-filling effect of nano-ceramic clay also helps to inhibit crack propagation and pore formation, making the ceramic layer denser and enhancing its heat resistance, insulation, and airtightness.

[0061] In summary, the synergistic effect of wollastonite mineral fibers and modified nano-ceramic not only improves the ceramicization properties of the material, but also enhances its mechanical properties, fire resistance, and flame retardancy, while ensuring processing and flexibility, making it suitable for applications in high flame-retardant and environmentally friendly cable sheaths.

[0062] In one specific implementation, the composite flame retardant A is an intumescent flame retardant composite material, which includes iron oxide, zinc borate, sepiolite, and modified ammonium polyphosphate.

[0063] In this embodiment, iron oxide acts as a catalytic carbonization agent, promoting the formation of a carbon layer in the polyolefin matrix at high temperatures. Zinc borate has smoke-suppressing and ceramic-aiding effects. Sepiolite fiber, as an inorganic skeleton reinforcing agent, significantly improves the density and crack resistance of the ceramic layer. Modified ammonium polyphosphate is the main intumescent flame retardant, releasing phosphate compounds upon heating to form a heat-insulating, intumescent carbon layer, while simultaneously promoting the ceramicization reaction together with glass powder and wollastonite.

[0064] In this application, the simplest method to improve the flame retardancy of polyolefin materials is to add flame retardants. Specifically, this invention selects ammonium polyphosphate, which can be used as both an acid source and a gas source in intumescent flame retardants. It can effectively suppress the smoke generated during polymer combustion, conforming to the trends of green, environmentally friendly, smoke-suppressing, and highly efficient flame retardancy. However, ammonium polyphosphate, as an inorganic substance, has poor compatibility when added to polyolefin materials and easily absorbs moisture from the air, which then migrates to the material surface and causes loss, resulting in a reduction in the mechanical properties and flame retardant efficiency of the polymer. Therefore, this invention also modifies ammonium polyphosphate to improve its hydrophobicity and thermal stability, thereby improving the flame retardant performance of polyolefin materials.

[0065] In a preferred embodiment, the modified ammonium polyphosphate is prepared as follows:

[0066] Ammonium polyphosphate was dispersed in a mixture of anhydrous ethanol and deionized water at a mass ratio of 2:1, with 20g of ammonium polyphosphate prepared per 100ml of the mixed solution.

[0067] Add ammonia to adjust the pH of the mixed solution to 10;

[0068] Phenylacetyltrimethoxysilane and tetraethyl orthosilicate were added to the mixed solution and stirred evenly with a glass beaker. The mass ratio of ammonium polyphosphate, phenyltrimethoxysilane and tetraethyl orthosilicate was 5:1:1.

[0069] The mixed solution was stirred at 40°C for 3 hours, then filtered and washed with anhydrous ethanol.

[0070] The washed powder was placed in a Soxhlet extractor and extracted with anhydrous ethanol for 24 hours. After drying in an electric heating oven, modified ammonium polyphosphate powder was obtained.

[0071] In this invention, modified ammonium polyphosphate releases phosphoric acid to form a thermally insulating expansion layer, which simultaneously absorbs some heat and suppresses smoke generation, aligning with green and environmentally friendly trends. An expandable, thermally insulating carbon layer is formed on the surface of the polyolefin matrix, simultaneously acting as an acid source to catalyze polymer carbonization. This layer synergistically promotes ceramic densification with wollastonite fibers, sepiolite fibers, and glass powder. Surface modification enhances its hydrophobicity and interfacial compatibility, reducing migration and precipitation, thereby significantly improving the material's flame retardant properties, smoke suppression effect, high-temperature mechanical strength, and long-term stability.

[0072] Example 1

[0073] This example provides a ceramicized polyolefin material for use as an outer sheath of a cable, the ceramicized polyolefin material comprising the following components in parts by weight:

[0074]

[0075] For details regarding the raw material ratios and preparation methods of modified nano-ceramic clay and composite flame retardant A, please refer to the above description.

[0076] Example 2

[0077] This example 2 provides a ceramicized polyolefin material for use as an outer sheath of a cable, the ceramicized polyolefin material comprising the following components in parts by weight:

[0078]

[0079]

[0080] For details regarding the raw material ratios and preparation methods of modified nano-ceramic clay and composite flame retardant A, please refer to the above description.

[0081] Example 3

[0082] This example three provides a ceramicized polyolefin material for use as an outer sheath of a cable, the ceramicized polyolefin material comprising the following components in parts by weight:

[0083]

[0084] For details regarding the raw material ratios and preparation methods of modified nano-ceramic clay and composite flame retardant A, please refer to the above description.

[0085] The product performance test results of the ceramicized polyolefin material in Example 2 are as follows:

[0086] The preparation of ceramicized polyolefin composite materials involves three steps. The first step is mixing, which is carried out in a Banbury mixer. The Banbury mixer is preheated, and a certain mass of matrix resin particles and filler powder are weighed into two beakers. When the Banbury mixer is heated to 160°C, the matrix resin is poured in. After the matrix resin is mixed evenly, the powder is slowly added to the Banbury mixer. After the filler and matrix resin are mixed for 20 minutes, the mixture is taken out and chopped while hot. The second step is vulcanization, which is carried out in a flat vulcanizing machine. The pressure is set to 10 MPa and preheated to 160°C. An appropriate amount of the mixed and chopped material is weighed and piled into a shape that is higher in the middle and lower around the edges. It is placed in a mold of appropriate thickness and vulcanized in the flat vulcanizing machine. The material is preheated for 10 minutes to melt it and remove air bubbles. The pressing temperature is 160°C. After hot pressing for 20 minutes and cold pressing for 20 minutes, the composite material is taken out after cooling to room temperature. The final step is sample preparation. After vulcanization, the material is cut into sample pieces of a specified shape on a stamping machine according to different testing standards, and then tested.

[0087] (1) Limiting Oxygen Index Test

[0088] An oxygen index specimen is injection molded using a micro injection molding machine with an oxygen index mold. Then, a 50mm mark is made on the specimen, and the oxygen index is observed when the specimen just reaches the mark after 3 minutes of combustion.

[0089] (2) Vertical Burning Test (UL 94)

[0090] Vertical combustion specimens were injection molded using a micro injection molding machine with a vertical combustion mold, and then placed on a vertical combustion tester for vertical combustion testing. Each formulation underwent 5 experiments.

[0091] (3) Mechanical property testing

[0092] The test was conducted according to the standard GB / T 1040—2006. The sample size was a dumbbell shape of 125mm×6mm×2mm (the width of the middle part was 5.5mm). The test speed was 50mm / min, and each sample was subjected to 5 tensile tests.

[0093] The product performance is shown in Table 1 after testing:

[0094] Sample Limiting oxygen index / % UL94 rating Tensile strength Elongation at break Ceramified polyolefin material 32.7％ V-0 13.58 MPa 132.58％

[0095] In a preferred embodiment, the inner sheath is extruded over the first flame-retardant wrapping tape layer using a ceramicized silicone rubber material. The ceramicized silicone rubber material comprises the following components in parts by weight:

[0096]

[0097] In one specific embodiment, the composite flame retardant B is a mixture of inorganic hydroxide, antimony trioxide, and magnesium aluminum carbonate layered double hydroxide, wherein the mass ratio of the inorganic hydroxide, antimony trioxide, and magnesium aluminum carbonate layered double hydroxide is 5:1:3. Through the composite flame retardant, the oxygen index of the product's adhesive can reach above 36.

[0098] In this application, methyl vinyl silicone rubber provides an elastic matrix and high-temperature resistance. Precipitated silica serves as a reinforcing material, improving mechanical strength and abrasion resistance while also enhancing thermal stability. Hydroxyl silicone oil is used to improve processing performance and flowability, while also increasing crosslinking uniformity. Wollastonite acts as a reinforcing, insulating, and refractory agent, contributing to the formation of a protective layer during the ceramization process. Glass powder is used to enhance the hardness and heat resistance of the ceramized structure. DHBP (bis-2-hydroxyphenyl-propane) acts as a crosslinking accelerator, increasing the crosslinking density of the silicone rubber. TAIC (tracene propyl isocyanurate) assists in crosslinking, improving heat resistance and aging resistance.

[0099] The ceramicized silicone rubber material of this invention meets the B1 flammability rating. The product performance test results are as follows:

[0100] The preparation of the ceramicized silicone rubber material of the present invention includes three steps. The first step is mixing, which is carried out in a mixer or open mill. The mixer is preheated to 70°C. A certain mass of methyl vinyl silicone rubber and filler powder (silica, wollastonite, composite flame retardant B, and glass powder) are weighed into two beakers. When the mixer reaches the set temperature, the silicone rubber is poured in first. After it is mixed evenly, the powder is slowly added and the mixing continues for 30 minutes until the filler is fully dispersed. Then, hydroxyl silicone oil is added and the mixing continues evenly. Subsequently, the mixture is cooled to below 60°C and DHBP and TAIC are added and mixed at low temperature for a short time. Finally, the mixed rubber is taken out while hot and vacuum degassed for 30 minutes. The second step is vulcanization, which is carried out in a flat vulcanizing machine. The pressure is set to 10 MPa, and the vulcanizing machine is preheated to 170°C. An appropriate amount of the mixed and degassed rubber material is weighed and piled into a shape that is higher in the middle and lower around the edges. It is then placed into a mold of appropriate thickness. Preheating is performed for 10 minutes to melt the material and remove air bubbles. Then, hot pressure vulcanization is applied for 15 minutes, followed by cold pressure for 20 minutes. After cooling to room temperature, the molded silicone rubber material is removed. The final step is sample preparation. The vulcanized material is cut into sample pieces of the specified shape on a sheet forming machine according to different testing standards for performance testing.

[0101] (1) The UL94 vertical flammability rating of the samples was tested according to Method B of GB / T 10707-2008 Determination of the flammability of rubber. The sample size was 130×13×3mm, and there were 5 samples in a group.

[0102] (2) Vitrification strength: Tested according to GB / T6569-2006, using a three-point bending fixture with a span of 40 mm and a beam moving speed of 0.5 mm / min. The bending strength of the test specimen is taken as its vitrification strength. The median value is taken after testing 5 specimens in parallel. The sample size is 70 mm × 6 mm × 4 mm. It is placed in a high-temperature box furnace, heated to the target temperature at 3 °C / min and kept at that temperature for a certain time before being naturally cooled to room temperature and taken out.

[0103] (3) Smoke density test: The smoke density level of the test specimens was tested in accordance with GB / T 8627-2007 Test Method for Smoke Density of Building Materials Combustion or Decomposition. The test specimen size was 25×25×3mm, and three specimens were tested in a group.

[0104] The product performance, after testing, is shown in Tables 2 and 3:

[0105] Table 2. Vertical combustion test results of ceramicized silicone rubber materials

[0106]

[0107] Table 3 Performance test results of ceramicized silicone rubber materials

[0108]

[0109] In one specific implementation, the metal sheath layer is a corrugated aluminum sleeve.

[0110] In one specific embodiment, the composite cable core includes a plurality of insulated cores, each insulated core including a conductor and an insulating layer covering the outer surface of the conductor; wherein, the insulating layer is a polyvinyl chloride sheath extruded onto the conductor.

[0111] Specifically, the conductor is either the first conductor structure or the second conductor structure in GB / T 3956.

[0112] In a preferred embodiment, an oxygen-barrier filler is used between the composite cable core and the first flame-retardant wrapping tape layer. The oxygen-barrier filler is fireproof putty that is semi-extruded onto the composite cable core.

[0113] In this field, fire-retardant putty for cables uses magnesium hydroxide as the main inorganic flame-retardant matrix. Upon heating, it absorbs heat, decomposes, releases water of crystallization, and generates a magnesium oxide layer, thereby lowering the temperature and forming an oxygen barrier. Expandable fillers such as expanded vermiculite, sepiolite, or expanded graphite are added to allow the material to expand in volume at high temperatures, forming a porous insulating layer. Appropriate amounts of inorganic binders (such as water glass or silica sol) are added to the fire-retardant putty to enhance its plasticity and molding strength at room temperature. Furthermore, to improve application and long-term stability, small amounts of organic modifiers or moisture-proofing agents (such as silane coupling agents or polyacrylates) can be added, along with inert fillers (such as talc or calcium carbonate) to adjust rheological properties and cost. The overall system rapidly expands into a shell upon heating, absorbing heat and cooling while isolating oxygen, thus achieving excellent fire-resistant sealing and flame-retardant effects.

[0114] Specifically, the raw material composition of the fireproof putty, by weight, includes 60 parts magnesium hydroxide as the main flame-retardant matrix; 10 parts expanded vermiculite or sepiolite; 5 parts water glass or silica sol as an inorganic binder; 5 parts talc or calcium carbonate to adjust rheology and reduce costs; 1 part silane coupling agent or polyacrylate organic modifier to improve interfacial bonding and moisture-proof performance; and 2 parts expanded graphite to improve the density and heat insulation of the carbon layer.

[0115] In one specific implementation, the water-blocking wrapping tape layer is formed by wrapping water-blocking tape. Both the first and second flame-retardant wrapping tape layers are made of mica tape, fiberglass tape, or composite flame-retardant polyester tape, and their flame-retardant temperature can reach above 750℃.

[0116] This invention verifies the performance of halogen-free, low-smoke, flame-retardant polyolefin cables, testing the insulation and sheath mechanical properties, insulation electrical properties, and conducting short-circuit integrity tests on the insulated cores, fire resistance tests, and combustion tests on the finished cables. The outer sheath is made of the ceramicized polyolefin material described in Example 2.

[0117] (1) A 3000V×5min withstand voltage test was conducted on the halogen-free, low-smoke flame-retardant polyolefin cable. A 2500V×5min water immersion withstand voltage test and a 168h water immersion insulation resistance retention test were also performed on the insulated core. Test data: Withstand voltage test: No breakdown. Water immersion withstand voltage test: No breakdown. Insulation resistivity retention after 168h water immersion: 91%.

[0118] Therefore, it can be seen that the water immersion insulation resistance retention rates of the halogen-free, low-smoke, flame-retardant polyolefin cables of the present invention are very close, indicating that the cables have strong moisture resistance.

[0119] (2) Simulate the stable high current required for a short circuit in the test cable using the test equipment, causing the conductor to melt within 3 seconds after energization. The test is conducted at (25±5)℃. The sample is placed in the test environment for at least 24 hours. Cut an insulated core with a length of (200±5)mm, and strip 30-35mm of insulation from both ends. Fix both ends to the current terminals of the test equipment. Turn on the power switch of the test equipment and observe whether the tested insulated core conductor melts or the insulation catches fire at high temperature. If any of the above occurs, the power switch should be turned off immediately to ensure the safety of the test equipment.

[0120] The test results show that when the insulated core sample of this work is short-circuited and melted, the insulation layer remains intact and undamaged, without cracking or ignition.

[0121] (3) B1 flame retardant characteristics requirements: A comprehensive combustion performance test was conducted on the two materials and the cable products made from these materials. The test results are shown in Table 4.

[0122] Table 4. Test results of the combustion performance of finished cables

[0123] As shown in Table 4, the performance of halogen-free, low-smoke flame-retardant polyolefin cables meets the requirements of GB 51298—2018 "Fire Protection Design Standard for Metros" for power control circuits in fire-resistant applications.

[0124]

[0125] Other structures of the halogen-free, low-smoke, flame-retardant polyolefin cable described in this embodiment are available in the prior art.

[0126] In the embodiments of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "at least one" refers to one or more, and the term "multiple" refers to two or more, unless otherwise expressly defined.

[0127] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A halogen-free, low-smoke, flame-retardant polyolefin cable, characterized in that, The composite cable core, the first flame-retardant wrapping tape layer, the inner sheath, the second flame-retardant wrapping tape layer, the water-blocking layer, the metal sheath layer and the outer sheath are sequentially arranged from inside to outside. The outer sheath is made of a ceramicized polyolefin material extruded and covered on the metal sheath layer.

2. A halogen-free, low-smoke, flame-retardant polyolefin cable according to claim 1, characterized in that, The ceramicized polyolefin material comprises the following components in parts by weight:

3. The halogen-free low-smoke flame-retardant polyolefin cable according to claim 2, characterized in that: The composite flame retardant A is an intumescent flame-retardant composite material, and the intumescent flame-retardant composite material comprises iron oxide, zinc borate, sepiolite and modified ammonium polyphosphate.

4. A halogen-free, low-smoke, flame-retardant polyolefin cable according to claim 3, characterized in that, The preparation method of the modified ammonium polyphosphate is as follows: The ammonium polyphosphate is dispersed in a mixed solution of anhydrous ethanol and deionized water, the mass ratio of the anhydrous ethanol and the deionized water is 2:1, and 20g of the ammonium polyphosphate is added per 100ml of the mixed solution; Ammonia water is added to adjust the PH of the mixed solution to 10; Phenyltrimethoxysilane and tetraethyl orthosilicate are added to the mixed solution, and the mixed solution is stirred uniformly with a glass cup, the mass ratio of the ammonium polyphosphate, the phenyltrimethoxysilane and the tetraethyl orthosilicate is 5:1:1; The mixed solution is stirred and reacted at 40℃ for 3h, and then filtered and washed with anhydrous ethanol; The washed powder is placed in a Soxhlet extractor and extracted with anhydrous ethanol for 24h, and then dried in an electric heating air drying oven to obtain the modified ammonium polyphosphate powder.

5. The halogen-free low-smoke flame-retardant polyolefin cable according to claim 1, characterized in that: The inner sheath is made of a ceramicized silicone rubber material extruded and covered on the first flame-retardant wrapping tape layer.

6. The halogen-free low-smoke flame-retardant polyolefin cable according to claim 5, characterized in that: The ceramicized silicone rubber material comprises the following components in parts by weight:

7. The halogen-free low-smoke flame-retardant polyolefin cable according to claim 6, characterized in that: The composite flame retardant B is a mixture of inorganic hydroxide, antimony trioxide and magnesium-aluminum carbonate hydrotalcite, and the mass ratio of the inorganic hydroxide, the antimony trioxide and the magnesium-aluminum carbonate hydrotalcite is 5:1:

3.

8. The halogen-free low-smoke flame-retardant polyolefin cable according to claim 1, characterized in that: The composite cable core comprises a plurality of insulated wire cores, and each insulated wire core comprises a conductor and an insulation layer wrapped outside the conductor. The insulation layer is a polyvinyl chloride sheath material extruded on the conductor.

9. The halogen-free low-smoke flame-retardant polyolefin cable according to claim 8, characterized in that: An oxygen barrier filler is filled between the composite cable core and the first flame-retardant wrapping tape layer, and the oxygen barrier filler is fire clay extruded and covered on the composite cable core by semi-extrusion.

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