A double-layer cable protection sleeve and a preparation method and application thereof

Abstract

The present application relates to a kind of double-layer cable protection sleeve and its preparation method and application, the double-layer cable protection sleeve includes gas production inner layer and carbon formation outer layer;The gas production inner layer includes resin matrix A, metal hydrate flame retardant and sheet nano filler A;The carbon formation outer layer includes resin matrix B, intumescent flame retardant and sheet nano filler B.The present application is structured and formula design to cable protection sleeve, utilize the difference of two layers of material decomposition temperature realizes combustion timing cooperation, to dynamically construct thick porous heat shield, solve the problem that traditional single-layer high filling flame-retardant sheath carbon layer is easy to peel off, gas dissipation direction is uncontrollable, and the problem of low flame-retardant efficiency, realizes the self-reinforced flame-retardant protection of combustion trigger type under the premise of not relying on superhigh filling amount.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant cable technology, and in particular to a double-layer cable protective sheath, its preparation method, and its application. Background Technology

[0002] Current cable flame retardant technologies are mainly divided into two paths: additive flame retardancy and intumescent flame retardancy. Additive flame retardancy commonly uses metal hydrates (such as aluminum hydroxide and magnesium hydroxide) as fillers, which inhibit combustion by absorbing heat and releasing water vapor upon thermal decomposition. This approach is effective for low flame retardant requirements (such as Class B and Class C), but it has significant limitations: to achieve a high flame retardant effect, the filler content usually needs to exceed 60%, leading to a significant decrease in sheath tensile strength and elongation at break. Furthermore, high-filler materials are difficult to extrude, easily resulting in surface roughness, delamination, and other defects. More importantly, a single hydrate system cannot pass the stringent bundled burning test, as the flame can still spread along the cable surface.

[0003] Intumescent flame retardants (IFRs, such as ammonium polyphosphate, pentaerythritol, and melamine) form an expanded carbon layer upon heating, isolating oxygen and heat, resulting in higher flame retardant efficiency. However, traditional single-layer IFR sheaths often face the problem of insufficient mechanical strength of the carbon layer during actual combustion. Flame erosion or thermal stress can easily cause the carbon layer to crack and peel off, exposing the unprotected material underneath. Some improvements attempt to add glass fibers or layered fillers to the intumescent flame retardant to reinforce the carbon layer, but this often sacrifices the material's flexibility and processing fluidity.

[0004] However, existing technologies also employ composite functional layers with structures such as "inner layer carbonization, outer layer gas generation" or "inner layer heat insulation, outer layer flame retardancy." However, in structures where the inner layer is an intumescent flame retardant layer and the outer layer is a metal hydrate layer, the outer layer releases water vapor first when heated, and the gas escapes outward, failing to effectively act on the inner carbon layer, thus the carbon layer cannot be inflated and strengthened. Conversely, if the gas generation layer is placed in the inner layer and the carbonization layer in the outer layer, the matching of the decomposition temperatures of the two layers and the control of the gas escape direction must be addressed.

[0005] In summary, existing cable flame retardant technologies either rely on high filler content at the expense of mechanical properties, or employ a single expansion system that makes the carbon layer prone to failure, or involve simple double-layer stacking without functional timing coordination, making it difficult to achieve the comprehensive goal of "low filler content, high efficiency, non-brittle sheath, and self-reinforcing carbon layer".

[0006] Therefore, how to provide a double-sheathed flame-retardant cable based on combustion timing coordination has become an urgent problem to be solved. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a double-layer cable protection sheath, its preparation method, and its application. By designing the structure and formula of the cable protection sheath, the difference in decomposition temperatures of the two layers of materials is utilized to achieve synergistic combustion timing, thereby dynamically constructing a thick and porous heat insulation barrier. This solves the problems of easy peeling of the carbon layer, uncontrollable gas escape direction, and low flame retardant efficiency in traditional single-layer high-filling flame-retardant sheaths. It achieves combustion-triggered self-reinforcing flame-retardant protection without relying on ultra-high filling amounts.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a double-layer cable protection sleeve, the double-layer cable protection sleeve comprising a gas-generating inner layer and a carbon-forming outer layer; the gas-generating inner layer comprising a resin matrix A, a metal hydrate flame retardant and a sheet-like nanofiller A; the carbon-forming outer layer comprising a resin matrix B, an intumescent flame retardant and a sheet-like nanofiller B.

[0009] Preferably, the thermal decomposition temperature of the gas-producing inner layer is 300-400℃, for example, it can be 300℃, 320℃, 340℃, 350℃, 360℃, 380℃ or 400℃, etc.

[0010] Preferably, the carbonization temperature of the carbonized outer layer is 270-350℃, for example, it can be 270℃, 290℃, 300℃, 320℃, 340℃ or 350℃.

[0011] This invention provides a double-layer cable protection sheath with a "combined combustion sequence" technical effect. The carbon-forming outer layer uses an intumescent flame retardant, which preferentially carbonizes at a relatively low temperature (270-350℃) to form a dense and continuous carbon skeleton. The gas-generating inner layer uses a metal hydrate flame retardant, which decomposes and releases inert gases (water vapor, nitrogen, etc.) at a relatively high temperature (300-400℃). When the cable encounters a flame, the carbon-forming outer layer forms a carbon layer first, followed by the decomposition and release of gas from the gas-generating inner layer. The gas cannot escape outward at the sealed interlayer interface and expands radially inward and outward. Due to the constraint of the outer carbon layer, the gas mainly drives the outer carbon layer to expand, thicken, and densify outward, forming a thick, porous, heat-insulating carbon foam. This solves the problems of easy peeling of the carbon layer and low flame-retardant efficiency in traditional flame-retardant sheaths, achieving combustion-triggered self-reinforcing flame-retardant protection. Incorporating sheet-like nanofillers into the gas-generating inner layer and the carbon-forming outer layer allows for the formation of dense and tortuous mass transfer channels through the stacking of these sheets. This effectively slows down the rapid diffusion of flammable and inert gases generated during high-temperature pyrolysis along the interior of the material. If the inner and outer layers of the protective sleeve do not contain sheet-like nanofillers, the high-temperature gases generated inside can easily escape smoothly along the axial direction, failing to create sufficient internal pressure between the layers. This significantly weakens the radial blowing and compaction effect on the carbonized layer, making it difficult to construct a continuous and dense heat-insulating and fire-retardant carbon layer. Ultimately, this results in a significant decrease in the overall fireproof, heat-insulating, and flame-retardant protective performance.

[0012] Preferably, the gas-generating inner layer comprises, by weight, 100 parts of resin matrix A, 160-200 parts of metal hydrate flame retardant, and 1-5 parts of sheet-like nanofiller A.

[0013] Among them, 160-200 portions can be, for example, 160 portions, 165 portions, 170 portions, 175 portions, 180 portions, 185 portions, 190 portions, 195 portions, or 200 portions; 1-5 portions can be, for example, 1 portion, 2 portions, 3 portions, 4 portions, or 5 portions.

[0014] Preferably, the resin matrix A comprises linear low-density polyethylene and / or ethylene-vinyl acetate copolymer.

[0015] Preferably, the resin matrix A comprises a combination of linear low-density polyethylene and ethylene-vinyl acetate copolymer.

[0016] Preferably, the mass ratio of the linear low-density polyethylene and the ethylene-vinyl acetate copolymer is 1:(0.25-0.67), for example, it can be 1:0.25, 1:0.3, 1:0.4, 1:0.5, 1:0.6 or 1:0.67, etc.

[0017] This invention uses linear low-density polyethylene (LLDPE) and ethylene-vinyl acetate copolymer (EVA) as the base resin for cable sheaths. Leveraging the high strength, wear resistance, and environmental stress cracking resistance of LLDPE, and combining it with the excellent flexibility, low-temperature toughness, and good wetting and dispersing ability of the polar groups of EVA on inorganic flame-retardant powders, this invention overcomes the shortcomings of single resins. While ensuring the mechanical strength, wear resistance, and extrusion processing performance of the cable sheath, it significantly improves low-temperature crack resistance, bending resistance, and weather aging resistance. Furthermore, it allows for high-filling of halogen-free flame retardants, achieving the preparation of low-smoke, halogen-free, highly flexible, and long-life cable protective sheaths.

[0018] Preferably, the VA content in the ethylene-vinyl acetate copolymer is 20-30% by mass, for example, it can be 20%, 22%, 24%, 25%, 26%, 28% or 30%, etc.

[0019] Preferably, the metal hydrate flame retardant comprises modified aluminum hydroxide.

[0020] Preferably, the modified aluminum hydroxide includes silanized aluminum hydroxide.

[0021] Preferably, the raw materials for preparing the silanized aluminum hydroxide include a silane coupling agent and aluminum hydroxide.

[0022] Preferably, the silane coupling agent includes KH-550.

[0023] Preferably, the mass ratio of the silane coupling agent to aluminum hydroxide is 1:(100-140), for example, it can be 1:100, 1:110, 1:120, 1:130 or 1:140, etc.

[0024] Preferably, the metal hydrate flame retardant further includes magnesium hydroxide.

[0025] Preferably, the metal hydrate flame retardant comprises a combination of modified aluminum hydroxide and magnesium hydroxide.

[0026] Preferably, the mass ratio of the modified aluminum hydroxide to magnesium hydroxide is 1:(0.01-0.2), for example, it can be 1:0.01, 1:0.05, 1:0.1, 1:0.15 or 1:0.2, etc.

[0027] This invention uses a combination of modified aluminum hydroxide and magnesium hydroxide as a metal hydrate flame retardant. It leverages the advantages of their matching thermal decomposition temperature gradients, synergistic heat absorption and cooling, and enhanced smoke suppression and carbonization to improve the shortcomings of single metal hydrates, such as low flame retardant efficiency, large addition amounts, and significant deterioration of the mechanical and processing properties of the substrate. At the same time, aluminum hydroxide undergoes surface modification treatment to reduce the surface polarity of the powder, improve the interfacial compatibility and dispersion uniformity with the polymer matrix, and reduce powder agglomeration. It can impart excellent flame retardant, smoke suppression, and anti-dripping properties to the material at a low addition amount. Moreover, it is halogen-free, low in toxicity, and does not produce corrosive fumes during combustion, making it more environmentally friendly and suitable for various applications.

[0028] Preferably, the sheet-like nanofiller A comprises sheet-like organomontmorillonite.

[0029] Preferably, the gas-generating inner layer further comprises, by weight, 1-5 parts of foaming nucleating agent, 10-30 parts of compatibilizer A, 1-2 parts of lubricant A, and 0.1-1 parts of antioxidant A.

[0030] Among them, 10-30 portions can be, for example, 10 portions, 15 portions, 20 portions, 25 portions, or 30 portions; 1-2 portions can be, for example, 1 portion, 1.2 portions, 1.4 portions, 1.5 portions, 1.6 portions, 1.8 portions, or 2 portions; 0.1-1 portion can be, for example, 0.1 portions, 0.2 portions, 0.4 portions, 0.5 portions, 0.6 portions, 0.8 portions, or 1 portion; 1-5 portions can be, for example, 1 portion, 2 portions, 3 portions, 4 portions, or 5 portions.

[0031] The addition of foaming nucleating agent and sheet-like nanofiller A to the gas-generating inner layer can optimize the formation of "uniform and fine bubbles" and "radial directional expansion". If the foaming nucleating agent is not added to the gas-generating inner layer, the bubbles will be large and uneven after foaming, the carbon layer will expand unevenly, and the flame retardant rating will be reduced.

[0032] Preferably, the compatibilizer A comprises polyethylene grafted with maleic anhydride.

[0033] Preferably, the lubricant A comprises zinc stearate.

[0034] Preferably, antioxidant A includes antioxidant 1010.

[0035] Preferably, the foaming nucleating agent comprises nano-silica.

[0036] Preferably, the carbonized outer layer comprises, by weight, 100 parts of resin matrix B, 80-120 parts of intumescent flame retardant, and 1-5 parts of sheet-like nanofiller B.

[0037] Among them, 80-120 portions can be, for example, 80 portions, 90 portions, 100 portions, 110 portions, or 120 portions; 1-5 portions can be, for example, 1 portion, 2 portions, 3 portions, 4 portions, or 5 portions.

[0038] Preferably, the resin matrix B comprises a combination of linear low-density polyethylene and ethylene-vinyl acetate copolymer.

[0039] Preferably, the mass ratio of the linear low-density polyethylene and the ethylene-vinyl acetate copolymer is 1:(0.25-0.67), for example, it can be 1:0.25, 1:0.3, 1:0.4, 1:0.5, 1:0.6 or 1:0.67, etc.

[0040] Preferably, the intumescent flame retardant comprises a combination of ammonium polyphosphate, pentaerythritol, and melamine.

[0041] Preferably, the degree of polymerization of the ammonium polyphosphate is >1000, for example, it can be 1100, 1200, 1400, 1500, 1600, 1800 or 2000.

[0042] Preferably, the mass ratio of ammonium polyphosphate, pentaerythritol and melamine is 1:(0.2-0.6):(0.2-0.6).

[0043] Among them, 0.2-0.6 can be, for example, 0.2, 0.3, 0.4, 0.5 or 0.6, etc.

[0044] Preferably, the sheet-like nanofiller B comprises sheet-like organomontmorillonite.

[0045] In this invention, the intumescent flame retardant is composed of ammonium polyphosphate, pentaerythritol, and melamine. Ammonium polyphosphate acts as the acid source, pentaerythritol as the char source, and melamine as the gas source, synergistically constructing an acid-char-gas intumescent flame retardant system. Ammonium polyphosphate decomposes upon heating, releasing phosphoric acid, which acts as the acid source for catalytic dehydration and carbonization. Pentaerythritol, a polyol char source, dehydrates and crosslinks under acidic conditions to form a carbon-rich framework. Melamine decomposes upon heating, releasing inert gas, which acts as the gas source for foaming and expansion. The three components work synergistically upon heating to form a porous, dense, intumescent carbon layer on the material surface, providing insulation, oxygen barrier, smoke suppression, prevention of molten dripping, and blocking the escape of combustible small molecules, achieving highly efficient halogen-free flame retardancy.

[0046] Preferably, the carbonized outer layer further comprises, by weight, 10-30 parts of compatibilizer B, 1-2 parts of lubricant B, 0.1-1 parts of antioxidant B, and 1-5 parts of carbonization reinforcing agent.

[0047] Among them, 10-30 portions can be 10 portions, 15 portions, 20 portions, 25 portions, or 30 portions, etc.; 1-2 portions can be 1 portion, 1.2 portions, 1.4 portions, 1.5 portions, 1.6 portions, 1.8 portions, or 2 portions, etc.; 0.1-1 portion can be 0.1 portions, 0.2 portions, 0.4 portions, 0.5 portions, 0.6 portions, 0.8 portions, or 1 portion, etc.; 1-5 portions can be 1 portion, 2 portions, 3 portions, 4 portions, or 5 portions, etc.

[0048] Preferably, the compatibilizer B comprises polyethylene grafted maleic anhydride.

[0049] Preferably, the lubricant B comprises calcium stearate.

[0050] Preferably, antioxidant B includes antioxidant 1010.

[0051] Preferably, the carbonization enhancer comprises zinc borate.

[0052] In this invention, the addition of flake-shaped organomontmorillonite serves as both a physical barrier and a carbon layer reinforcement in both the inner and outer layers, but with different focuses. In the gas-producing inner layer, it mainly guides the radial expansion of gas and prevents axial escape; in the carbon-forming outer layer, it acts as a "skeleton" to enhance the density and erosion resistance of the carbon layer, preventing cracking and peeling.

[0053] In a second aspect, the present invention provides a method for preparing a double-layer cable protective sheath as described in the first aspect, the method comprising the following steps: (1) Mix the components of the gas-producing inner layer to obtain the gas-producing inner layer mixture; The components that form the carbon outer layer are mixed to obtain the carbon outer layer mixture; (2) The gas-producing inner layer mixture and the carbon-forming outer layer mixture are co-extruded in two layers to obtain the double-layer cable protection sleeve.

[0054] Preferably, the extrusion temperature of the gas-generating inner layer mixture in the double-layer co-extrusion molding is 150-170℃ (e.g., 150℃, 155℃, 160℃, 165℃ or 170℃, etc.), and the extrusion temperature of the carbon-forming outer layer mixture is 140-160℃ (e.g., 140℃, 145℃, 150℃, 155℃ or 160℃, etc.).

[0055] Thirdly, the present invention provides a cable comprising a double-layer cable protection sheath as described in the first aspect.

[0056] Preferably, the cable comprises, from the inside out, a conductor, an insulation layer, optionally a filler, a wrapping tape, an inner lining, an armor layer, and a double-layer cable protection sheath as described in the first aspect.

[0057] The conductor adopts a compacted round conductor structure conforming to Class 2 of GB / T 3956-2008, and its composition, performance, and appearance comply with the requirements of GB / T 3956-2008. The conductor surface is smooth, free of oil stains, burrs that could damage the shielding and insulation, sharp edges, and protruding or broken single wires. The insulation material can be cross-linked polyethylene, and its performance and nominal thickness meet the requirements of GB / T 12706.1-2020. The cross-section of the insulation layer is free of visible defects such as bubbles and pinholes. The cable can be a single-core cable or a multi-core cable. Multi-core cables can be two-core, three-core, four-core, or five-core cables. When the cable is a multi-core cable, the insulation layer wraps around the outside of the conductor, and filler fills the gap between the multi-core cable core and the wrapping tape. The filler is made of low-smoke halogen-free flame-retardant polypropylene (PP) filler rope for dense filling, making the multi-core cable round. The filler rope should be non-hygroscopic and have a certain flame-retardant ability. After filling, a layer of high flame-retardant, low-smoke, halogen-free tape (such as alkali-free fiberglass tape) is wrapped around the inner lining, with an overlap rate of ≥30%. The inner lining serves as an isolation layer, and its thickness conforms to the requirements of GB / T 12706.1-2020. Materials suitable for the cable's operating temperature, such as polyethylene or halogen-free low-smoke polyolefin, can be used. The armor layer enhances the cable's tensile and compressive strength and protects the gas-producing inner layer from mechanical damage. For single-core cables, the armor layer uses a double-layer gap wrapping with non-magnetic metal tape or non-magnetic metal wire armor. For multi-core cables, the armor layer uses a double-layer gap wrapping with galvanized steel tape or galvanized steel wire armor. The gap in the inner metal tape is covered by the outer metal tape near the middle, with a gap ratio not exceeding 50% of the metal tape width. The wrapping is smooth and electrically continuous. The thickness of the armor layer and the specifications of the steel wire conform to the requirements of GB / T 12706.1-2020. The double-layer cable protection sheath is extruded and installed on the outer layer of the armor layer. The gas-generating inner layer is close to the armor layer, and the carbon-forming outer layer is far away from the armor layer.

[0058] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The double-layer cable protection sleeve developed in this invention constructs a unique mechanism of first forming a skeleton and then inflating for self-reinforcement; its charred outer layer can achieve dynamic carbon deposition and thickening during combustion, which changes the disadvantage of traditional materials that are only passively eroded, and effectively solves the industry pain points of easy detachment of flame-retardant carbon layer and low flame-retardant performance. This invention solves the contradiction of the formulation of traditional single-layer system that needs to take into account both high flame-retardant filling and high charring performance through the dual-layer functional partition design of gas-producing inner layer and charred outer layer; the amount of filler added to the overall system can be flexibly adjusted, and the comprehensive mechanical properties such as tensile strength and elongation at break of the material are largely preserved. At the same time, the gas generated by the thermal decomposition of gas-producing inner layer forms directional radial expansion under the binding effect of charred outer layer, which restricts the disorderly escape of gas along the axial direction, reduces the loss of flame-retardant performance, and further improves the overall flame-retardant protection effect.

[0059] (2) The double-layer cable protective sheath of the present invention is prepared by a double-layer co-extrusion one-time molding process, which does not require modification of the original main structure of the cable. The process adaptability is strong and the production cost is easy to control. The finished cable of the present invention meets the basic requirements of GB / T 12706.1-2020 standard, such as structural dimensions, mechanical properties before aging, high temperature pressure, carbon black content, and heat shrinkage, and has excellent single vertical combustion and bundled Class A combustion performance. Attached Figure Description

[0060] Figure 1 This is a cross-sectional structural diagram of the cable provided by the present invention; Among them, 1-conductor, 2-insulating layer, 3-filler, 4-wrapping tape, 5-inner liner, 6-armoring layer, 7-gas-generating inner layer, and 8-carbonized outer layer. Detailed Implementation

[0061] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0062] The silanized aluminum hydroxide used in the following examples and comparative examples was prepared by the following method: KH-550 (1.5 g) was mixed with aluminum hydroxide (180 g) and reacted at 110 °C for 20 min to obtain the silanized aluminum hydroxide.

[0063] Example 1 This embodiment provides a double-layer cable protective sleeve and its preparation method, wherein the double-layer cable protective sleeve includes a gas-generating inner layer and a carbon-forming outer layer; The gas-producing inner layer comprises, by weight, 70 parts linear low-density polyethylene, 30 parts ethylene-vinyl acetate copolymer, 180 parts silanized aluminum hydroxide, 10 parts magnesium hydroxide, 20 parts polyethylene grafted maleic anhydride, 2 parts flake organomontmorillonite, 3 parts nano silica, 1.5 parts zinc stearate, and 0.5 parts antioxidant 1010. The carbonized outer layer comprises, by weight, 70 parts linear low-density polyethylene, 30 parts ethylene-vinyl acetate copolymer, 55 parts ammonium polyphosphate, 25 parts pentaerythritol, 20 parts melamine, 20 parts polyethylene grafted with maleic anhydride, 3 parts flake organomontmorillonite, 4 parts zinc borate, 1.5 parts calcium stearate, and 0.5 parts antioxidant 1010; The preparation method includes: (1) Mix the components of the gas-producing inner layer to obtain the gas-producing inner layer mixture; The components that form the carbon outer layer are mixed to obtain the carbon outer layer mixture; (2) The gas-generating inner layer mixture and the carbon-forming outer layer mixture are co-extruded in two layers (the extrusion temperature of the gas-generating inner layer mixture is 160°C and the extrusion temperature of the carbon-forming outer layer mixture is 150°C) to obtain the double-layer cable protection sleeve.

[0064] Example 2 This embodiment provides a double-layer cable protective sleeve and its preparation method, wherein the double-layer cable protective sleeve includes a gas-generating inner layer and a carbon-forming outer layer; The gas-producing inner layer comprises, by weight, 80 parts of linear low-density polyethylene, 20 parts of ethylene-vinyl acetate copolymer, 190 parts of silanized aluminum hydroxide, 10 parts of magnesium hydroxide, 30 parts of polyethylene grafted maleic anhydride, 5 parts of flake organomontmorillonite, 5 parts of nano silica, 2 parts of zinc stearate, and 1 part of antioxidant 1010. The carbonized outer layer comprises, by weight, 80 parts of linear low-density polyethylene, 20 parts of ethylene-vinyl acetate copolymer, 50 parts of ammonium polyphosphate, 15 parts of pentaerythritol, 15 parts of melamine, 30 parts of polyethylene grafted maleic anhydride, 5 parts of sheet-like organomontmorillonite, 5 parts of zinc borate, 2 parts of calcium stearate, and 1 part of antioxidant 1010; The preparation method includes: (1) Mix the components of the gas-producing inner layer to obtain the gas-producing inner layer mixture; The components that form the carbon outer layer are mixed to obtain the carbon outer layer mixture; (2) The gas-generating inner layer mixture and the carbon-forming outer layer mixture are co-extruded in two layers (the extrusion temperature of the gas-generating inner layer mixture is 170°C and the extrusion temperature of the carbon-forming outer layer mixture is 160°C) to obtain the double-layer cable protection sleeve.

[0065] Example 3 This embodiment provides a double-layer cable protective sleeve and its preparation method, wherein the double-layer cable protective sleeve includes a gas-generating inner layer and a carbon-forming outer layer; The gas-producing inner layer comprises, by weight, 60 parts of linear low-density polyethylene, 40 parts of ethylene-vinyl acetate copolymer, 160 parts of silanized aluminum hydroxide, 10 parts of polyethylene grafted maleic anhydride, 1 part of flake organomontmorillonite, 1 part of nano silica, 1 part of zinc stearate, and 0.2 parts of antioxidant 1010. The carbonized outer layer comprises, by weight, 60 parts linear low-density polyethylene, 40 parts ethylene-vinyl acetate copolymer, 60 parts ammonium polyphosphate, 30 parts pentaerythritol, 30 parts melamine, 10 parts polyethylene grafted with maleic anhydride, 1 part flake organomontmorillonite, 1 part zinc borate, 1 part calcium stearate, and 0.2 parts antioxidant 1010; The preparation method includes: (1) Mix the components of the gas-producing inner layer to obtain the gas-producing inner layer mixture; The components that form the carbon outer layer are mixed to obtain the carbon outer layer mixture; (2) The gas-generating inner layer mixture and the carbon-forming outer layer mixture are co-extruded in two layers (the extrusion temperature of the gas-generating inner layer mixture is 150°C and the extrusion temperature of the carbon-forming outer layer mixture is 140°C) to obtain the double-layer cable protection sleeve.

[0066] Example 4 This embodiment provides a double-layer cable protection sleeve and its preparation method. The difference from Embodiment 1 is that the gas-generating inner layer does not contain nano-silica.

[0067] Comparative Example 1 This comparative example provides a cable protective sleeve and its preparation method, which differs from Example 1 in that the cable protective sleeve only contains a gas-generating inner layer.

[0068] Comparative Example 2 This comparative example provides a cable protective sleeve and its preparation method, which differs from Example 1 in that the cable protective sleeve only contains a carbonized outer layer.

[0069] Comparative Example 3 This comparative example provides a double-layer cable protection sleeve and its preparation method, which differs from Example 1 in that: the gas-generating inner layer comprises, by weight, 70 parts of linear low-density polyethylene, 30 parts of ethylene-vinyl acetate copolymer, 1.5 parts of zinc stearate, and 0.5 parts of antioxidant 1010; the carbon-forming outer layer comprises, by weight, 70 parts of linear low-density polyethylene, 30 parts of ethylene-vinyl acetate copolymer, 1.5 parts of calcium stearate, and 0.5 parts of antioxidant 1010.

[0070] Comparative Example 4 This comparative example provides a double-layer cable protection sleeve and its preparation method. The difference from Example 1 is that the gas-generating inner layer does not contain flake-shaped organic montmorillonite.

[0071] Comparative Example 5 This comparative example provides a double-layer cable protection sleeve and its preparation method, which differs from Example 1 in that the carbonized outer layer does not contain flaky organic montmorillonite.

[0072] Application Example 1 This application example provides a cable and a method for its fabrication, such as... Figure 1 As shown, the cable comprises, from the inside out, a conductor 1, an insulation layer 2, a filler 3, a wrapping tape 4, an inner lining layer 5, an armor layer 6, and a double-layer cable protection sleeve (including a gas-generating inner layer 7 and a carbon-forming outer layer 8) provided in Example 1.

[0073] The preparation method includes: The cable core uses 2.57 mm oxygen-free copper monofilaments, and 19 oxygen-free copper monofilaments are twisted into copper strands in a 1+6+12 structure using a concentric stranding machine; silane cross-linked polyethylene is extruded over the outside of the cable core; four strands of the cable core after the insulation layer is extruded are taken, and the gaps between the cable cores are filled with low-smoke halogen-free flame-retardant polypropylene (PP) filler rope, and after filling, a layer of fiberglass wrapping tape is wrapped around it with an overlap rate of ≥30%; polyethylene is then extruded over the wrapping tape to form an inner lining layer; galvanized steel wire is then wrapped around the inner lining layer to form an armor layer; and the double-layer cable protection sheath provided in Example 1 is then extruded over the armor layer, with the gas-producing inner layer close to the armor layer and the carbonized outer layer far away from the armor layer (the extrusion temperature of the gas-producing inner layer mixture is 150℃, and the extrusion temperature of the carbonized outer layer mixture is 160℃), thus obtaining the cable.

[0074] Application Example 2-4 and Comparison Application Example 1-5 Application Examples 2-4 and Comparative Application Examples 1-5 each provide a cable and its preparation method. The difference from Application Example 1 is that the double-layer cable protective sleeve provided in Example 1 is replaced with the double-layer cable protective sleeve or cable protective sleeve provided in Examples 2-4 and Comparative Examples 1-5, respectively.

[0075] Comparative Application Example 6 This comparative application example provides a cable and its manufacturing method, which differs from Application Example 1 in that: in the double-layer cable protective sheath, the carbonized outer layer is disposed on the side close to the armor layer, and the gas-generating inner layer is disposed on the side far away from the armor layer.

[0076] Test methods The cables provided in the corresponding use cases and comparative application examples underwent the following performance tests: (1) Single vertical burning test: The test shall be conducted in accordance with GB / T 18380.12-2022; (2) Bundle Class A combustion test: The test shall be conducted in accordance with GB / T 18380.33-2022.

[0077] The test results are shown in Table 1: Table 1 The test results show that: (1) As can be seen from Application Examples 1 to 4, the present invention can construct a continuous, dense, and erosion-resistant expanded carbon layer with a low amount of flame retardant filling through a sequential synergistic structural design of “carbonization of the outer layer first and gas production of the inner layer later”, which significantly improves the flame retardant and fireproof performance of the cable and meets the requirements for use of high-grade flame retardant cables. The cables produced can all pass the single vertical burning test and the bundled Class A burning test.

[0078] (2) By comparing Application Example 1 with Application Example 1-2, it can be seen that if a single-layer sheath structure is used, the resulting cable can only pass through single vertical combustion and cannot pass through bundled Class A combustion. This indicates that the setting of a single gas-generating layer or a single carbon-forming layer is difficult to simultaneously take into account the stability of the carbon layer and the gas blowing enhancement effect.

[0079] (3) As can be seen from Application Example 1 and Comparative Application Example 3, if the gas-generating inner layer and the carbon-forming outer layer lack a flame-retardant system (including flame-retardant components and sheet-like nanofillers), the cable cannot form a continuous and dense heat-insulating carbon layer when it burns. The resin matrix continues to decompose under heat and releases a large amount of combustible gas. The flame easily spreads rapidly along the surface of the sheath. The carbon layer has extremely low strength and is very easy to fall off. It cannot effectively block heat and oxygen, and the overall flame-retardant protection capability is basically lost. It cannot pass the bundled burning test.

[0080] (4) As can be seen from Application Example 1 and Comparative Application Examples 4-5, sheet-like nanofillers can significantly suppress axial gas escape, enhance radial expansion and densification of carbon layers, and are an important technical means to improve flame retardant efficiency. If either the gas-producing inner layer or the carbon-forming outer layer lacks sheet-like nanofillers, the resulting cable will not pass the bundled combustion test.

[0081] (5) As can be seen from Application Example 1 and Comparative Application Example 6, if the gas-producing inner layer and carbon-forming outer layer double-layer structure are arranged in reverse, the resulting cable will also fail the bundled Class A combustion test. The reverse structure setting will cause the gas to escape outward and the carbon layer will not be effectively thickened and strengthened, resulting in the failure of flame retardant protection.

[0082] The applicant declares that the above description is only a specific application of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A double-layer cable protection sleeve, characterized in that, The double-layer cable protection sheath includes a gas-generating inner layer and a carbon-forming outer layer; the gas-generating inner layer includes a resin matrix A, a metal hydrate flame retardant, and a sheet-like nanofiller A; the carbon-forming outer layer includes a resin matrix B, an intumescent flame retardant, and a sheet-like nanofiller B.

2. The double-layer cable protection sleeve according to claim 1, characterized in that, The thermal decomposition temperature of the gas-producing inner layer is 300-400℃; Preferably, the carbonization temperature of the carbonized outer layer is 270-350℃.

3. The double-layer cable protection sleeve according to claim 1 or 2, characterized in that, The gas-generating inner layer comprises, by weight, 100 parts of resin matrix A, 160-200 parts of metal hydrate flame retardant, and 1-5 parts of sheet-like nanofiller A.

4. The double-layer cable protection sleeve according to any one of claims 1-3, characterized in that, The resin matrix A comprises linear low-density polyethylene and / or ethylene-vinyl acetate copolymer; Preferably, the resin matrix A comprises a combination of linear low-density polyethylene and ethylene-vinyl acetate copolymer; Preferably, the mass ratio of the linear low-density polyethylene to the ethylene-vinyl acetate copolymer is 1:(0.25-0.67). Preferably, the mass content of VA in the ethylene-vinyl acetate copolymer is 20-30%; Preferably, the metal hydrate flame retardant comprises modified aluminum hydroxide; Preferably, the modified aluminum hydroxide includes silanized aluminum hydroxide; Preferably, the raw materials for preparing the silanized aluminum hydroxide include a silane coupling agent and aluminum hydroxide; Preferably, the silane coupling agent includes KH-550; Preferably, the mass ratio of the silane coupling agent to aluminum hydroxide is 1:(100-140). Preferably, the metal hydrate flame retardant further includes magnesium hydroxide; Preferably, the metal hydrate flame retardant comprises a combination of modified aluminum hydroxide and magnesium hydroxide; Preferably, the mass ratio of the modified aluminum hydroxide to magnesium hydroxide is 1:(0.01-0.2). Preferably, the sheet-like nanofiller A comprises sheet-like organomontmorillonite.

5. The double-layer cable protection sleeve according to any one of claims 1-4, characterized in that, The gas-producing inner layer further includes, by weight, 1-5 parts of foaming nucleating agent, 10-30 parts of compatibilizer A, 1-2 parts of lubricant A, and 0.1-1 parts of antioxidant A; Preferably, the compatibilizer A comprises polyethylene grafted with maleic anhydride; Preferably, the lubricant A comprises zinc stearate; Preferably, antioxidant A includes antioxidant 1010; Preferably, the foaming nucleating agent comprises nano-silica.

6. The double-layer cable protection sleeve according to any one of claims 1-5, characterized in that, The carbonized outer layer comprises, by weight, 100 parts of resin matrix B, 80-120 parts of intumescent flame retardant, and 1-5 parts of sheet-like nanofiller B; Preferably, the resin matrix B comprises a combination of linear low-density polyethylene and ethylene-vinyl acetate copolymer; Preferably, the mass ratio of the linear low-density polyethylene to the ethylene-vinyl acetate copolymer is 1:(0.25-0.67). Preferably, the intumescent flame retardant comprises a combination of ammonium polyphosphate, pentaerythritol, and melamine; Preferably, the degree of polymerization of the ammonium polyphosphate is >1000; Preferably, the mass ratio of ammonium polyphosphate, pentaerythritol, and melamine is 1:(0.2-0.6):(0.2-0.6). Preferably, the sheet-like nanofiller B comprises sheet-like organomontmorillonite.

7. The double-layer cable protection sleeve according to any one of claims 1-6, characterized in that, The carbonized outer layer further includes, by weight, 10-30 parts of compatibilizer B, 1-2 parts of lubricant B, 0.1-1 parts of antioxidant B, and 1-5 parts of carbonization reinforcing agent; Preferably, the compatibilizer B comprises polyethylene grafted with maleic anhydride; Preferably, the lubricant B comprises calcium stearate; Preferably, antioxidant B includes antioxidant 1010; Preferably, the carbonization enhancer comprises zinc borate.

8. A method for preparing a double-layer cable protective sheath as described in any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) Mix the components of the gas-producing inner layer to obtain the gas-producing inner layer mixture; The components that form the carbon outer layer are mixed to obtain the carbon outer layer mixture; (2) The gas-producing inner layer mixture and the carbon-forming outer layer mixture are co-extruded in two layers to obtain the double-layer cable protection sleeve.

9. The method for preparing a double-layer cable protective sheath according to claim 8, characterized in that, In the bilayer co-extrusion molding process, the extrusion temperature of the gas-producing inner layer mixture is 150-170℃, and the extrusion temperature of the carbon-forming outer layer mixture is 140-160℃.

10. A cable, characterized in that, The cable includes a double-layer cable protection sleeve as described in any one of claims 1-7.

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