Low smoke self-extinguishing flame retardant optical cable

Abstract

The application belongs to the technical field of optical cables, and provides a low-smoke self-extinguishing flame-retardant optical cable, wherein the cladding sheath comprises, from outside to inside, an outer sheath, a non-metallic fiber layer, a smoke absorption layer, an inner sheath and a water-blocking layer; the cable core comprises a fire extinguishing unit, a steel belt, an optical unit and a central reinforcing unit, the steel belt is an integral whole in the circumferential direction and is wrapped around the periphery of all the optical units, the outer periphery of the steel belt forms spaced concave surfaces and convex surfaces, the fire extinguishing unit is filled in the concave surfaces of the steel belt, the smoke absorption layer is used to adsorb volatile substances generated in the combustion process, the fire extinguishing unit is used to release fire extinguishing agents to further play a flame-retardant effect, the steel belt is used to wrap temperature-resistant optical units, so that the internal optical units are completely isolated from flame combustion, smoke cannot overflow, and the special cable core structure and cladding sheath structure design can effectively reduce the smoke emission and prevent the flame from spreading to the cable core, thereby ensuring smooth transmission performance.

Description

Technical Field

[0001] This application relates to the field of optical cable technology, and in particular to a low-smoke, self-extinguishing, flame-retardant optical cable. Background Technology

[0002] Optical fiber cables are communication cable assemblies that use one or more optical fibers encased in a protective sheath as the transmission medium. With the rapid development of my country's telecommunications services, optical fiber cables, as a crucial carrier of fiber optic communication technology, play a vital role in the increasingly information-driven society. While users enjoy the convenience brought by fiber optic digital transmission, they are also affected by the frequent occurrence of various fire accidents. Therefore, ensuring sufficient time for rescue operations in the event of a fire, minimizing losses to personal safety, property, and information security, and maintaining the integrity of the optical fiber cable line are extremely important.

[0003] According to statistics from the fire department, fires involving electrical wires, cables, or fiber optic cables account for approximately 40% of all building fires. Furthermore, about 80% of deaths in fires are due to poisoning from toxic gases, suffocation from pervasive smoke, or being unable to escape due to lack of visibility. Therefore, using non-toxic, harmless, and highly flame-retardant materials or specially designed structures in fiber optic cables for communication lines minimizes or eliminates the production of toxic and harmful gases and smoke during combustion, thus reducing the damage caused by fires. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a low-smoke, self-extinguishing, flame-retardant optical cable.

[0005] In a first aspect, embodiments of this application provide a low-smoke, self-extinguishing, flame-retardant optical cable, comprising a cable core and a sheathing layer covering the cable core. The sheathing layer, from the outside in, comprises an outer sheath, a non-metallic fiber layer, a smoke-absorbing layer, an inner sheath, and a water-blocking layer. The smoke-absorbing layer comprises two graphene films and activated carbon particles located between the two graphene films. The cable core comprises a fire-extinguishing unit, a steel strip, an optical unit, and a central reinforcement unit. The central reinforcement unit is located at the center of the optical cable and extends along the length of the optical cable. The optical units are twisted around the periphery of the central reinforcement unit. The steel strip is a single unit circumferentially wrapped around all the optical units. The outer periphery of the steel strip forms spaced concave and convex surfaces. The fire-extinguishing unit fills the concave surface of the steel strip.

[0006] In some embodiments, the outer surface of the steel strip between two adjacent optical units forms a concave surface, and the outer surface of the steel strip at the optical unit forms a convex surface; there are multiple fire extinguishing units in the concave surface, the fire extinguishing unit at the deepest part of the concave surface has the largest volume, and the volumes of the fire extinguishing units on both sides of the deepest part of the concave surface along the circumferential direction of the cable core decrease sequentially until the entire gap between the concave surface and the water-blocking layer is filled by the fire extinguishing units.

[0007] In some embodiments, the maximum distance from the outermost edge of the fire extinguishing unit in each concave surface to the central axis of the optical cable is greater than the distance from the outermost edge of the convex surface to the central axis of the optical cable. That is, the height of the concave surface after the fire extinguishing unit is filled is higher than that of the convex surface, and the wall thickness of the inner sheath near the convex surface is greater than that of the inner sheath near the concave surface.

[0008] In some embodiments, the non-metallic fiber layer is woven from multiple strands of non-metallic fibers, and the non-metallic fiber layer has at least two layers to form a honeycomb structure.

[0009] In some embodiments, the steel strip is longitudinally wrapped without overlapping, and the two sides are aligned and welded to form a closed cavity.

[0010] In some embodiments, the fire extinguishing unit is covered with a thin-walled plastic layer and filled with a fire extinguishing agent.

[0011] In some embodiments, the extinguishing agent is at least one of the following: a mixture of flame-retardant ultrafine solid powders with a particle size ≤0.5μm, a nano-substrate composite metal oxide, an inert gas, and a non-flammable gas.

[0012] In some embodiments, the activated carbon particles are ultrafine activated carbon particles with a particle size of 0.5 μm to 20 μm.

[0013] In some embodiments, the optical unit comprises, from the outside to the inside, a first plastic layer, a fire-resistant layer, a second plastic layer, a water-blocking material, and an optical fiber. The heat distortion temperature, thermal decomposition temperature, and melting point of the first plastic layer are all greater than those of the second plastic layer. The fire-resistant layer is a polyimide composite tape coated with mica powder. The first plastic layer, the fire-resistant layer, and the second plastic layer are formed by three-layer co-extrusion. The water-blocking material is water-blocking yarn.

[0014] In some embodiments, the outer protective layer and the inner protective layer employ two different low-smoke flame-retardant materials. The first low-smoke flame-retardant material of the outer protective layer has a maximum specific optical density of 25 to 55 during flaming combustion, and the second low-smoke flame-retardant material of the inner protective layer has a maximum specific optical density of 125 to 250 during flameless combustion.

[0015] In some embodiments, the first low-smoke flame retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 5%–8% halogenated aromatic polymer resin, 15%–25% flame retardant, 5%–10% flame retardant additive, 5%–8% smoke suppressant, and 5%–8% other additives; the halogenated aromatic polymer resin is a bromine-containing aromatic polymer; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

[0016] In some embodiments, the second low-smoke flame retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 15%–25% flame retardant, 5%–8% flame retardant additive, 8%–15% smoke suppressant, 5%–8% other additives, and 0.5%–2% graphene oxide; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

[0017] In some embodiments, the flame retardant and flame retardant additive are flame retardants and flame retardant additives pre-blended with phenolic resin or acrylic resin.

[0018] Secondly, this application also provides a low-smoke self-extinguishing flame-retardant optical cable, including a cable core and a sheath covering the cable core. The sheath includes an outer sheath and an inner sheath. The outer sheath and the inner sheath use two different low-smoke flame-retardant materials. The first low-smoke flame-retardant material of the outer sheath has a maximum specific optical density of 25 to 55 when burning with a flame, and the second low-smoke flame-retardant material of the inner sheath has a maximum specific optical density of 125 to 250 when burning without a flame.

[0019] In some embodiments, the first low-smoke flame retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 5%–8% halogenated aromatic polymer resin, 15%–25% flame retardant, 5%–10% flame retardant additive, 5%–8% smoke suppressant, and 5%–8% other additives; the halogenated aromatic polymer resin is a bromine-containing aromatic polymer; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

[0020] In some embodiments, the second low-smoke flame retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 15%–25% flame retardant, 5%–8% flame retardant additive, 8%–15% smoke suppressant, 5%–8% other additives, and 0.5%–2% graphene oxide; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

[0021] In some embodiments, the flame retardant and flame retardant additive are flame retardants and flame retardant additives pre-blended with phenolic resin or acrylic resin.

[0022] In some embodiments, the protective coating comprises, from the outside in, an outer protective layer, a non-metallic fiber layer, a smoking layer, an inner protective layer, and a water-blocking layer; the smoking layer comprises two graphene films and activated carbon particles located between the two graphene films.

[0023] In some embodiments, the non-metallic fiber layer is woven from multiple strands of non-metallic fibers, and the non-metallic fiber layer has at least two layers to form a honeycomb structure.

[0024] In some embodiments, the activated carbon particles are ultrafine activated carbon particles with a particle size of 0.5 μm to 20 μm.

[0025] In some embodiments, the cable core includes a fire extinguishing unit, a steel strip, an optical unit, and a central reinforcement unit. The central reinforcement unit is located at the center of the optical cable and extends along the length of the optical cable. The optical units are twisted around the periphery of the central reinforcement unit. The steel strip is a single unit in the circumferential direction, covering the periphery of all the optical units. The outer periphery of the steel strip forms spaced concave and convex surfaces. The fire extinguishing unit fills the concave surface of the steel strip.

[0026] In some embodiments, the outer surface of the steel strip between two adjacent optical units forms a concave surface, and the outer surface of the steel strip at the optical unit forms a convex surface; there are multiple fire extinguishing units in the concave surface, the fire extinguishing unit at the deepest part of the concave surface has the largest volume, and the volumes of the fire extinguishing units on both sides of the deepest part of the concave surface along the circumferential direction of the cable core decrease sequentially until the gap of the entire concave surface is filled by the fire extinguishing units.

[0027] In some embodiments, the maximum distance from the outermost edge of the fire extinguishing unit in each concave surface to the central axis of the optical cable is greater than the distance from the outermost edge of the convex surface to the central axis of the optical cable. That is, the height of the concave surface after the fire extinguishing unit is filled is higher than that of the convex surface, and the wall thickness of the inner sheath near the convex surface is greater than that of the inner sheath near the concave surface.

[0028] In some embodiments, the steel strip is longitudinally wrapped without overlapping, and the two sides are aligned and welded to form a closed cavity.

[0029] In some embodiments, the fire extinguishing unit is covered with a thin-walled plastic layer and filled with a fire extinguishing agent.

[0030] In some embodiments, the extinguishing agent is at least one of the following: a mixture of flame-retardant ultrafine solid powders with a particle size ≤0.5μm, a nano-substrate composite metal oxide, an inert gas, and a non-flammable gas.

[0031] In some embodiments, the optical unit comprises, from the outside to the inside, a first plastic layer, a fire-resistant layer, a second plastic layer, a water-blocking material, and an optical fiber. The heat distortion temperature, thermal decomposition temperature, and melting point of the first plastic layer are all greater than those of the second plastic layer. The fire-resistant layer is a polyimide composite tape coated with mica powder. The first plastic layer, the fire-resistant layer, and the second plastic layer are formed by three-layer co-extrusion. The water-blocking material is water-blocking yarn.

[0032] The beneficial effects that this application can achieve.

[0033] This application provides a low-smoke, self-extinguishing, flame-retardant optical cable with excellent flame-retardant and self-extinguishing capabilities. The sheathing layer, from the outside to the inside, includes an outer sheath, a non-metallic fiber layer, a smoke-absorbing layer, an inner sheath, and a water-blocking layer. The smoke-absorbing layer comprises two layers of graphene film and activated carbon particles between them. Utilizing the large specific surface area of ​​graphene and activated carbon particles, they have excellent adsorption capacity, making it easier to adsorb volatiles generated during combustion and preventing their release and diffusion during combustion. The presence of the smoke-absorbing layer greatly reduces the amount of smoke emitted by the optical cable. At the same time, graphene does not burn when exposed to open flame and does not act as a combustion promoter; it can form a dense and continuous carbon layer, preventing oxygen from entering the interior of the optical cable. The cable core includes fire-extinguishing units, steel strips, optical units, and a central reinforcement unit. The steel strip is a single, circumferentially integral unit that covers the periphery of all the optical units. The outer circumference of the steel strip has alternating concave and convex surfaces. The fire-extinguishing units fill the concave surfaces of the steel strip. When the inner sheath is heated during combustion, heat is first transferred to the fire-extinguishing units. These units release extinguishing agents to lower the temperature or isolate oxygen, further enhancing flame retardancy and delaying or preventing the transfer of flame or heat to the optical units. The steel strip improves lateral pressure resistance and does not deform at high temperatures, preventing contact between the optical units and open flames. The steel strip covering the heat-resistant optical units completely isolates them from flame combustion, preventing smoke from escaping. This further ensures the stable structure of the optical units within a small space and reduces the risk of fiber embrittlement and breakage due to external environmental or mechanical stress. According to EN 61034-2 "Measurement of smoke density of cables burning under specified conditions - Part 2: Test procedures and requirements", this invention provides a low-smoke self-extinguishing flame-retardant optical cable with a light transmittance of not less than 85%, a total smoke production (TSP1200) of 1200s ≤ 45m2 and a peak smoke production rate (SPR) ≤ 0.20m2 / s.

[0034] Furthermore, this application provides a low-smoke self-extinguishing flame-retardant optical cable in which the inner and outer sheaths are made of materials with different components, giving them different specific optical densities and reducing the amount of smoke generated when the sheaths burn. The outer sheath typically burns with a flame; the material design of the first low-smoke flame-retardant material ensures that the outer sheath material produces relatively little smoke when burning with a flame. Since the inner sheath is difficult to directly contact with an open flame, it is equivalent to flameless combustion, in which case the amount of smoke would be relatively greater. This application, through the material design of the second low-smoke flame-retardant material used in the inner sheath, significantly reduces the amount of smoke generated by the inner sheath.

[0035] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This invention provides a structural schematic diagram of a low-smoke, self-extinguishing, flame-retardant optical cable.

[0038] Figure 2 A schematic diagram of the optical unit structure of a low-smoke self-extinguishing flame-retardant optical cable according to this application is shown.

[0039] Among them: 1-outer sheath, 2-non-metallic fiber layer, 3-smoking layer, 4-inner sheath, 5-water-blocking strip, 6-optical unit, 7-central reinforcement unit, 8-fire extinguishing unit, 9-stainless steel strip, 10-cable core, 11-concave surface, 12-convex surface, 13-first plastic layer, 14-fire-resistant layer, 15-second plastic layer, 16-optical fiber, 17-water-blocking material, 18-covering sheath. Detailed Implementation

[0040] The term "comprising" in the specification, claims, and accompanying drawings of this application is synonymous with "including," "containing," or "characterized in," and is inclusive of endpoints or open-ended, and does not exclude additional unstated elements or method steps. "Comprising" is a technical term used in the language of the claims, meaning that the stated element is present, but other elements may be added and still form a construction or method within the scope of the claims.

[0041] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance. In this application, the term "about" means encompassing minute variations (at most + / - 10%) of the stated value.

[0042] According to statistics from the fire department, fires involving electrical wires, cables, or fiber optic cables account for approximately 40% of all building fires. Furthermore, about 80% of deaths in fires are due to poisoning from toxic gases, suffocation from pervasive smoke, or being unable to escape due to lack of visibility. Therefore, using non-toxic, harmless, and highly flame-retardant materials or specially designed structures in fiber optic cables for communication lines minimizes or eliminates the production of toxic and harmful gases and smoke during combustion, thus reducing the damage caused by fires.

[0043] This application has discovered that a smoke extraction layer composed of graphene film and ultrafine activated carbon particles has excellent adsorption capacity, making it easier to adsorb volatiles generated during combustion and prevent their release and diffusion during combustion. Furthermore, graphene does not burn when exposed to open flame and does not act as a combustion aid. It can form a dense and continuous carbon layer, preventing oxygen from entering the optical cable and thus playing a flame-retardant role.

[0044] This application has discovered that the plastic material inside the cable core can produce smoke when burned. At the same time, the internal optical unit has poor positional stability, which can easily cause wear and even breakage of the optical fiber surface in a fire, affecting communication security during a fire. By using steel tape to cover the heat-resistant optical unit, the internal optical unit can be completely isolated from flame combustion, and smoke cannot escape. This further ensures that the optical unit maintains a stable structure in a small space and also reduces the risk of optical fiber embrittlement and breakage caused by external environmental or mechanical stress.

[0045] This application has discovered optical cables with two sheaths. Due to the special position of the inner sheath in the structure of the flame-retardant optical cable, it is difficult for it to come into direct contact with an open flame when the optical cable is burning. It is equivalent to flameless combustion. At this time, the amount of smoke will be relatively greater. Therefore, using a different material for the inner sheath than the outer sheath can reduce the amount of smoke.

[0046] To reduce smoke emission and improve the flame retardant performance of optical cables, this application provides a low-smoke, self-extinguishing, flame-retardant optical cable, comprising a cable core and a sheathing layer covering the cable core. The sheathing layer, from the outside in, includes an outer sheath, a non-metallic fiber layer, a smoke-emitting layer, an inner sheath, and a water-blocking layer. The smoke-emitting layer comprises two graphene films and activated carbon particles located between the two graphene films. The cable core includes a fire-extinguishing unit, a steel strip, optical units, and a central reinforcement unit. The central reinforcement unit is located at the center of the optical cable and extends along the length of the optical cable. The optical units are twisted around the periphery of the central reinforcement unit. The steel strip is a single unit circumferentially wrapped around all the optical units. The outer periphery of the steel strip forms spaced concave and convex surfaces, and the fire-extinguishing unit fills the concave surface of the steel strip.

[0047] This application provides a low-smoke, self-extinguishing, flame-retardant optical cable. The sheathing, from the outside in, includes an outer sheath, a non-metallic fiber layer, a smoke-absorbing layer, an inner sheath, and a water-blocking layer. The smoke-absorbing layer comprises two layers of graphene film and activated carbon particles between them. Utilizing the large specific surface area of ​​graphene and activated carbon particles, they have excellent adsorption capacity, making it easier to adsorb volatiles generated during combustion and preventing their release and diffusion during combustion. The presence of the smoke-absorbing layer significantly reduces the amount of smoke emitted by the optical cable. Simultaneously, graphene does not burn when exposed to an open flame and does not act as a combustion aid; it can form a dense and continuous carbon layer, preventing oxygen from entering the interior of the optical cable. The cable core includes fire-extinguishing units, steel strips, optical units, and a central reinforcement unit. The steel strip is a single, circumferentially integral unit that covers the periphery of all the optical units. The outer circumference of the steel strip has alternating concave and convex surfaces. The fire-extinguishing units fill the concave surfaces of the steel strip. When the inner sheath is heated during combustion, heat is first transferred to the fire-extinguishing units. These units release extinguishing agents to lower the temperature or isolate oxygen, further enhancing flame retardancy and delaying or preventing the transfer of flame or heat to the optical units. The steel strip improves lateral pressure resistance and does not deform at high temperatures, preventing contact between the optical units and open flames. The steel strip covering the heat-resistant optical units completely isolates them from flame combustion, preventing smoke from escaping. This further ensures the stable structure of the optical units within a small space and reduces the risk of fiber embrittlement and breakage due to external environmental or mechanical stress. According to EN 61034-2 "Measurement of smoke density of cables burning under specified conditions - Part 2: Test procedures and requirements", this invention provides a low-smoke self-extinguishing flame-retardant optical cable with a light transmittance of not less than 85%, a total smoke production (TSP1200) of 1200s ≤ 45m2 and a peak smoke production rate (SPR) ≤ 0.20m2 / s.

[0048] Other embodiments of this application also provide a low-smoke self-extinguishing flame-retardant optical cable, including a cable core and a sheath covering the cable core. The sheath includes an outer sheath and an inner sheath. The outer sheath and the inner sheath use two different low-smoke flame-retardant materials. The first low-smoke flame-retardant material of the outer sheath has a maximum specific optical density of 25 to 55 when burning with a flame, and the second low-smoke flame-retardant material of the inner sheath has a maximum specific optical density of 125 to 250 when burning without a flame.

[0049] In some other embodiments, the first low-smoke flame retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 5%–8% halogenated aromatic polymer resin, 15%–25% flame retardant, 5%–10% flame retardant additive, 5%–8% smoke suppressant, and 5%–8% other additives; the halogenated aromatic polymer resin is a bromine-containing aromatic polymer; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

[0050] In some other embodiments, the second low-smoke flame retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 15%–25% flame retardant, 5%–8% flame retardant additive, 8%–15% smoke suppressant, 5%–8% other additives, and 0.5%–2% graphene oxide; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

[0051] According to the low-smoke self-extinguishing flame-retardant optical cable provided in this application, the inner and outer sheaths are made of materials with different components, giving them different specific optical densities and reducing the amount of smoke generated when the sheaths burn. The outer sheath generally burns with a flame; through the material design of the first low-smoke flame-retardant material, the amount of smoke generated by the outer sheath material during flaming combustion can be ensured to be relatively small. Since the inner sheath is difficult to directly contact with an open flame, it is equivalent to flameless combustion, in which case the amount of smoke generated would be relatively larger. In this application, through the material design of the second low-smoke flame-retardant material used in the inner sheath, the amount of smoke generated by the inner sheath is greatly reduced.

[0052] In this application, the maximum specific optical density (Dm) is an important parameter for measuring the amount of smoke produced when a material burns, also known as the maximum smoke density. The higher the maximum specific optical density during combustion, the greater its smoke production, the denser the black smoke emitted during combustion, and the greater the environmental pollution.

[0053] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0054] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0055] Conventional optical cables are prone to producing toxic gases and fumes during disasters, which not only affects the evacuation of personnel at the accident site but also seriously hinders firefighters' rescue efforts. Therefore, environmentally friendly flame-retardant optical cables have become the preferred choice for home delivery optical cables. Flame-retardant optical cables refer to new types of optical cables that can delay ignition, reduce the speed of flame propagation, and extinguish the flame rapidly once the cable is removed from an external open flame.

[0056] This application provides a low-smoke, self-extinguishing, flame-retardant optical cable that uses sheath materials with different specific optical densities and adds a smoke-absorbing layer. In the event of a fire, it can effectively reduce the amount of smoke. At the same time, it adopts a special cable core structure and sheath structure design to prevent the flame from spreading to the cable core and ensure smooth transmission performance.

[0057] like Figure 1 As shown, this application provides a low-smoke, self-extinguishing, flame-retardant optical cable, including a cable core 10 and a sheathing layer 18 covering the cable core 10. The sheathing layer 18, from the outside to the inside, includes an outer sheath 1, a non-metallic fiber layer 2, a smoke-absorbing layer 3, an inner sheath 4, a water-blocking tape 5, and the cable core 10. The cable core 10 includes a fire-extinguishing unit 8, a stainless steel strip 9, optical units 6, and a central reinforcement unit 7. The central reinforcement unit 7 is located at the center of the optical cable and extends along the length of the optical cable. The optical units 6 are twisted around the periphery of the central reinforcement unit. The stainless steel strip 9 is a single unit circumferentially (it can be segmented along the extension direction of the optical cable, for example, multiple segments of stainless steel strip 9 connected end to end along the extension direction of the optical cable), covering the periphery of all the optical units 6. The outer periphery of the stainless steel strip 9 forms spaced concave surfaces 11 and convex surfaces 12, and the fire-extinguishing unit fills the concave surface of the stainless steel strip. The cable core 10 is formed by twisting together multiple fire extinguishing units 8 of different sizes and multiple optical units 6 of the same size around the central reinforcing unit 7. The optical units 6 are in close contact with each other and with the central reinforcing unit 7, but not directly with the fire extinguishing units 8. A complete stainless steel strip 9 covers the periphery of the multiple optical units 6, forming a compact structure with multiple concave surfaces 11 and multiple convex surfaces 12. The multiple fire extinguishing units 8 are arranged according to size and sequentially fill the concave surfaces 11 of the stainless steel strip 9.

[0058] In some other embodiments, the stainless steel strip 9 can also be replaced with other steel strips, such as galvanized steel strip, chrome-plated steel strip, etc.

[0059] The outer protective layer 1 uses a high-performance low-smoke flame retardant material, namely the first low-smoke flame retardant material. Through reasonable formulation or component design, the maximum specific optical density of the outer protective layer material is guaranteed to be 25 to 55 when burning with flame.

[0060] In this embodiment, the outer sheath uses a high-performance, low-smoke flame-retardant material comprising (parts by weight, percentage by weight): 35%–45% polyolefin base resin, 5%–8% halogenated aromatic polymer resin, 15%–25% flame retardant, 5%–10% flame retardant additives, 5%–8% smoke suppressant, and 5%–8% other additives. Polyolefin polymers, with their polyolefin carbon chains capable of cyclization, condensation, and graphitization into carbon particles, produce a higher smoke emission. Therefore, in the outer sheath, the content of polyolefin base resin is reduced, while the content of halogenated aromatic polymer resin is appropriately increased.

[0061] The polyolefin base resin refers to the polymer component in the polyolefin composition according to this application, which typically accounts for at least 90 wt% of the total composition. The performance of the low-smoke flame-retardant material of this application is independent of the type of polyolefin base resin used. Therefore, the polyolefin base resin can be any polyolefin or polyolefin composition. For example, the polyolefin base resin includes ethylene homopolymers or copolymers or propylene homopolymers or copolymers. For example, in some embodiments, the polyolefin base resin comprises at least two olefin homopolymers or copolymers with different weight-average molecular weights. For example, the polyolefin base resin is a composition of two or more different, compatible ethylene polymers and copolymers, such as two or more of VLDPE (very low density polyethylene) resin, EEA resin (ethylene-ethyl acrylate), EBA resin (ethylene-butyl acrylate), EPR resin (ethylene-propylene copolymer resin), and EPDM (ethylene propylene diene monomer rubber), blended and modified in a certain proportion. For example, the modified polyolefin base resin has a melt flow index (MFR) of 1.0–3.0 g / 10 min and a copolymer content of 35%–45%.

[0062] Halogenated aromatic polymer resins are bromine-containing aromatic polymers, such as brominated cross-linked polystyrene. Flame retardants are ultrafine metal hydroxide powders, such as at least one of magnesium hydroxide and aluminum hydroxide. Flame retardant additives are one or more of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate. Smoke suppressants are molybdenum-containing compounds. Commonly used molybdenum-containing compounds include one or more of molybdenum trioxide, ammonium octamolate, calcium molybdate, calcium phosphomolybdate, and zinc molybdate; they can also be molybdenum compounds combined with small amounts of antimony trioxide, copper oxide, iron oxide, cadmium oxide, etc. Other additives include at least one or more of compatibilizers, antioxidants, ultraviolet absorbers, and heat stabilizers.

[0063] Furthermore, in some embodiments, the flame retardant and flame retardant additive are pre-blended with phenolic resin or acrylic resin, thereby coating the flame retardant with resin, reducing the risk of dehydration or failure of the flame retardant during high-temperature processing, and improving the flame retardant effect.

[0064] In this application, the non-metallic fiber layer 2 can be an organic non-metallic fiber layer, such as an aramid fiber braided layer, a nylon fiber braided layer, a polyester fiber braided layer, etc. The non-metallic fiber layer 2 can also be an inorganic non-metallic fiber layer, such as a carbon fiber braided layer, a glass fiber braided layer, a mica fiber braided layer, a silicon carbide fiber braided layer, a boron fiber braided layer, a basalt fiber braided layer, a graphene fiber braided layer, etc. These non-metallic fibers have high specific strength and specific stiffness, good heat insulation, temperature resistance, electrical insulation and chemical stability, and long service life. The non-metallic fiber layer 2 can be woven from multiple strands of non-metallic fibers in two or more layers to form a honeycomb structure. For example, in some embodiments, it is woven from multiple strands of aramid fibers, at least two layers, forming a multi-layer honeycomb structure. The aramid fiber braided layer utilizes its fire-resistant properties—non-combustible, non-dripping, and non-smoke-producing—to form a non-metallic fire-resistant layer. When the temperature is too high, such as above 900℃, the aramid fiber braided layer will carbonize, forming a heat-resistant barrier that protects the inner cable core. Meanwhile, the aramid fiber braided layer also has wear-resistant and tear-resistant properties, providing additional mechanical protection for the optical cable.

[0065] In this application, the smoke-absorbing layer 3 is composed of a graphene film and ultrafine activated carbon particles. The graphene film consists of two layers, with the ultrafine activated carbon particles in the middle. The particle size of the ultrafine activated carbon particles is generally between 0.5 μm and 20 μm. Utilizing the large specific surface area of ​​graphene and ultrafine activated carbon particles, they possess excellent adsorption capacity, making it easier to adsorb volatiles generated during combustion and preventing their release and diffusion during combustion, especially in the inner sheath structure of the optical cable. Because the inner sheath is unlikely to directly contact an open flame when the optical cable burns, its smoke generation would be relatively greater. Therefore, the presence of the smoke-absorbing layer significantly reduces the smoke generation of the optical cable. Simultaneously, graphene does not burn when exposed to an open flame and does not act as a combustion promoter; it can form a dense and continuous carbon layer, preventing oxygen from entering the interior of the optical cable.

[0066] As noted in this application, due to the special position of the inner sheath in the flame-retardant optical cable structure, it is difficult for it to directly contact an open flame when the optical cable burns, which is equivalent to flameless combustion, resulting in a relatively larger amount of smoke. Therefore, the inner sheath 4 is made of a different material than the outer sheath 1, and the amount of smoke generated when the optical cable burns can be reduced by adjusting the material.

[0067] The inner protective layer 4 of this application adopts a high-performance low-smoke flame retardant material, namely the second low-smoke flame retardant material. Through reasonable formulation or component design, the maximum specific optical density of the inner protective layer material is guaranteed to be 125 to 250 when burning without flame.

[0068] For example, in some embodiments of this application, the material composition of the inner protective layer 4 includes, by weight percentage: 35% to 45% polyolefin base resin, 15% to 25% flame retardant, 5% to 8% flame retardant additive, 8% to 15% smoke suppressant, 5% to 8% other additives, and 0.5% to 2% graphene oxide.

[0069] The polyolefin base resin refers to the polymer component in the polyolefin composition according to this application, which typically accounts for at least 90 wt% of the total composition. The performance of the low-smoke flame-retardant material of this application is independent of the type of polyolefin base resin used. Therefore, the polyolefin base resin can be any polyolefin or polyolefin composition. For example, the polyolefin base resin includes ethylene homopolymers or copolymers or propylene homopolymers or copolymers. For example, in some embodiments, the polyolefin base resin comprises at least two olefin homopolymers or copolymers with different weight-average molecular weights. For example, the polyolefin base resin is a composition of two or more different, compatible ethylene polymers and copolymers, such as two or more of VLDPE (very low density polyethylene) resin, EEA resin (ethylene-ethyl acrylate), EBA resin (ethylene-butyl acrylate), EPR resin (ethylene-propylene copolymer resin), and EPDM (ethylene propylene diene monomer rubber), blended and modified in a certain proportion. For example, the modified polyolefin base resin has a melt flow index (MFR) of 1.0–3.0 g / 10 min and a copolymer content of 35%–45%. Flame retardants are ultrafine metal hydroxide powders, commonly including at least one of magnesium hydroxide and aluminum hydroxide. Flame retardant additives are one or more of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate. Smoke suppressants are molybdenum-containing compounds. Commonly used molybdenum-containing compounds include one or more of molybdenum trioxide, ammonium octamolate, calcium molybdate, calcium phosphomolybdate, and zinc molybdate; they can also be molybdenum compounds combined with small amounts of antimony trioxide, copper oxide, iron oxide, cadmium oxide, etc. Other additives include at least one or more of compatibilizers, antioxidants, ultraviolet absorbers, and heat stabilizers.

[0070] Graphene oxide (GO) is the oxide of graphene. It is brownish-yellow in color and is commonly available in powder, flake, and solution forms. For example, the graphene oxide prepared by Hangzhou Zhitai Purification Technology Co., Ltd. is a single-layer graphene oxide with an average thickness of 0.5-1.2 nm and a diameter of 4-7 μm. When graphene is combined with other traditional flame retardants, it can effectively leverage the advantages of both materials, exhibiting a good synergistic effect. The addition of graphene oxide can reduce the release of combustible gases and further suppress smoke generation.

[0071] In this application, the fire extinguishing unit 8 is filled in the concave surface 11 formed by two adjacent light units 6, and is separated from the light unit 6 by a stainless steel strip 9.

[0072] In some embodiments, depending on the size of the concave surface 11, each concave surface 11 has more than one fire extinguishing unit 8, and the sizes vary. The fire extinguishing unit 8 at the deepest point is the largest, and then the size decreases sequentially towards both sides, ensuring that the entire gap of the concave surface 11 is filled with fire extinguishing units 8. The height of the concave surface 11 after being filled will be significantly higher than that of the convex surface 12, resulting in a significant difference in the wall thickness of the inner protective layer 4 under a uniform inner protective layer diameter. That is, the wall thickness of the inner protective layer near the convex surface 12 is greater than that near the concave surface 11. The effect is that when the inner protective layer is heated during combustion, the heat will be transferred to the fire extinguishing unit 8 first, allowing the fire extinguishing unit 8 to function first, thereby protecting the internal light unit 6.

[0073] Fire extinguishing unit 8 uses a thin thermoplastic resin material to encapsulate the extinguishing agent. When heated, its thin-walled plastic layer breaks, releasing the extinguishing agent inside. Through the extinguishing agent's function of lowering the temperature or isolating oxygen, it further achieves a flame-retardant effect, delaying or preventing the transfer of flames or heat to the light unit.

[0074] In some embodiments, the extinguishing agent is a mixture of flame-retardant ultrafine solid powders with a particle size ≤0.5μm, such as a flame-retardant ultrafine solid powder with a particle size ≤0.5μm, including sodium bicarbonate or ammonium phosphate, magnesium stearate, silica powder, and talc. Its function is to decompose under high temperature, absorb heat, chemically inhibit flaming combustion, and suffocate flameless combustion.

[0075] In other embodiments, the extinguishing agent can be a nano-based composite metal oxide, such as nano-dihydroxy composite magnesium hydroxide material with a particle size ≤0.1μm. When heated, the composite metal oxide releases water of crystallization, evaporates, decomposes and releases water vapor, absorbing a large amount of combustion heat energy, thereby significantly reducing the surface temperature of the material, delaying or preventing the material from burning or thermally decomposing. At the same time, the huge specific surface area of ​​the nanoparticles can also suppress the material's smoke emission and reduce the smoke density.

[0076] In other embodiments, the extinguishing agent may also be an inert gas or a non-flammable gas, such as N2 or CO2, which reduces the oxygen content at the combustion site by releasing the gas, thereby preventing combustion.

[0077] The water layer in this application can be a water-blocking strip 5, which not only blocks water but also fixes the entire cable core.

[0078] The stainless steel strip 9 enhances resistance to lateral pressure and will not deform under high temperatures, preventing the light unit from contacting open flames. The stainless steel strip 9 is longitudinally wrapped without overlap, and the two sides are aligned and welded to form a closed cavity, completely isolating the internal light unit from flame combustion and preventing smoke from escaping.

[0079] The optical unit 6 in this application, such as Figure 2 As shown, from the outside in, the structure includes a first plastic layer 13, a fire-resistant layer 14, a second plastic layer 15, a water-blocking material 17, and an optical fiber 16. In terms of manufacturing process, the first plastic layer 13, the fire-resistant layer 14, and the second plastic layer 15 are co-extruded simultaneously, resulting in superior temperature resistance compared to conventional loose-sleeve tubing. Specifically, the heat distortion temperature, thermal decomposition temperature, and melting point of the first plastic layer 13 are all higher than those of the second plastic layer 15. For example, the material of the first plastic layer 13 may be nylon, FEP, ETFE, PFA, LCP, etc. Similarly, the material of the second plastic layer 15 may be PC, PE, PBT, LSZH, PVC, TPE, etc. The fire-resistant layer 14 is a polyimide composite tape coated with mica powder.

[0080] The optical fiber 16 has at least one core and is either single-mode or multimode. For example, it can be a bare fiber with a coating outer diameter of 200μm to 255μm, with common coating materials being acrylic resin or polyamide resin. Alternatively, it can be a coated optical fiber with a plastic coating and an outer diameter of 500μm to 1000μm, with common plastic layers being LSZH, PA, TPE, ETFE, PTFE, or FEP. Furthermore, in some other embodiments, the optical fiber 16 can be a heat-resistant optical fiber to accommodate the coating or plastic coating. For example, a heat-resistant optical fiber with a special polyester (polyimide coating) coating capable of withstanding temperatures up to 300°C.

[0081] Furthermore, in some embodiments, the multiple optical fibers 16 may be independent and dispersed within the optical unit 6. Alternatively, they may be arranged in a certain order and bound together by a suitable material to form a whole, the binding element including, but not limited to, an optical fiber bundle or an optical fiber ribbon.

[0082] Water-blocking material 17 is water-blocking yarn with a dry structure, which can reduce the use of grease and is clean and environmentally friendly.

[0083] It can be seen that the optical unit provided in this application has an overall thickness of 230μm to 600μm, which is similar to the thickness of the loose tube of conventional optical cable, but its heat resistance, flame retardancy, fire resistance and mechanical strength are significantly better than those of conventional loose tube.

[0084] The low-smoke, self-extinguishing, flame-retardant optical cable provided in this application has the following beneficial effects:

[0085] (1) The inner and outer protective layers are made of materials with different components to give them different specific light densities, thereby reducing the amount of smoke generated when the protective layer is burning.

[0086] (2) A smoke layer has been added to the optical cable structure to adsorb the volatiles generated during the combustion process and prevent their release and diffusion during the combustion process, especially the inner sheath structure of the optical cable covering it.

[0087] (3) The cable core structure with a special combination of fire extinguishing unit and optical unit can help the optical cable extinguish itself and protect the internal optical unit when the optical cable burns through the inner and outer sheaths.

[0088] (4) The stainless steel strip covering the heat-resistant optical unit can completely isolate the internal optical unit from flame combustion, and the smoke cannot escape. This further ensures that the optical unit maintains a stable structure in a small space, and also reduces the risk of optical fiber embrittlement and breakage caused by external environment or mechanical stress.

[0089] According to EN 61034-2 "Measurement of smoke density of cables burning under specified conditions - Part 2: Test procedures and requirements", this invention provides a low-smoke, self-extinguishing, flame-retardant optical cable with a light transmittance of not less than 85% and a total smoke production (TSP1200) ≤ 45m³ / s over 1200 seconds. 2 And the peak smoke production rate (SPR) is ≤0.20m. 2 / s.

[0090] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A low-smoke, self-extinguishing, flame-retardant optical cable, comprising a cable core and a sheathing layer covering the cable core, characterized in that, The coating layer comprises, from the outside to the inside, an outer protective layer, a non-metallic fiber layer, a smoking layer, an inner protective layer, and a water-blocking layer; the smoking layer comprises two graphene films and activated carbon particles located between the two graphene films. The cable core includes a fire extinguishing unit, a steel strip, an optical unit, and a central reinforcement unit. The central reinforcement unit is located at the center of the optical cable and extends along the length of the optical cable. The optical units are twisted around the periphery of the central reinforcement unit. The steel strip is a single unit along the circumference of the optical cable, covering the periphery of all the optical units. The outer periphery of the steel strip forms spaced concave and convex surfaces, and the fire extinguishing unit is filled within the concave surface of the steel strip. The outer protective layer and the inner protective layer employ two different low-smoke flame-retardant materials. The first low-smoke flame-retardant material of the outer protective layer has a maximum specific optical density of 25-55 during flaming combustion, while the second low-smoke flame-retardant material of the inner protective layer has a maximum specific optical density of 125-250 during flameless combustion. The first low-smoke flame-retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 5%–8% halogenated aromatic polymer resin, 15%–25% flame retardant, 5%–10% flame retardant additive, 5%–8% smoke suppressant, and 5%–8% other additives; the halogenated aromatic polymer resin is a bromine-containing aromatic polymer; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

2. The low-smoke self-extinguishing flame-retardant optical cable according to claim 1, characterized in that, The outer surface of the steel strip between two adjacent optical units forms a concave surface, and the outer surface of the steel strip at the optical unit forms a convex surface; there are multiple fire extinguishing units in the concave surface, the fire extinguishing unit at the deepest part of the concave surface has the largest volume, and the volumes of the fire extinguishing units on both sides of the deepest part of the concave surface along the circumferential direction of the cable core decrease sequentially.

3. The low-smoke self-extinguishing flame-retardant optical cable according to claim 1, characterized in that, The height of the concave surface after the fire extinguishing unit is filled is higher than that of the convex surface, and the wall thickness of the inner protective layer near the convex surface is greater than that of the inner protective layer near the concave surface.

4. The low-smoke self-extinguishing flame-retardant optical cable according to claim 1, characterized in that, The non-metallic fiber layer is woven from multiple strands of non-metallic fibers, and there are at least two layers of non-metallic fiber layer, forming a honeycomb structure.

5. The low-smoke self-extinguishing flame-retardant optical cable according to claim 1, characterized in that, The steel strip is longitudinally wrapped without overlapping, and the two sides are aligned and welded to form a closed cavity.

6. The low-smoke self-extinguishing flame-retardant optical cable according to claim 1, characterized in that, The fire extinguishing unit is covered with a thin-walled plastic layer and filled with fire extinguishing agent.

7. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 6, characterized in that, The extinguishing agent is at least one of the following: a mixture of flame-retardant ultrafine solid powders with a particle size ≤0.5μm, a nano-substrate composite metal oxide, an inert gas, or a non-flammable gas.

8. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 1, characterized in that, The activated carbon particles are ultrafine activated carbon particles with a particle size of 0.5 μm to 20 μm.

9. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 1, characterized in that, The optical unit comprises, from the outside to the inside, a first plastic layer, a fire-resistant layer, a second plastic layer, a water-blocking material, and an optical fiber. The heat distortion temperature, thermal decomposition temperature, and melting point of the first plastic layer are all greater than those of the second plastic layer. The fire-resistant layer is a polyimide composite tape coated with mica powder. The first plastic layer, the fire-resistant layer, and the second plastic layer are formed by co-extrusion of three layers simultaneously. The water-blocking material is water-blocking yarn.

10. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 1, characterized in that, The second low-smoke flame-retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 15%–25% flame retardant, 5%–8% flame retardant additive, 8%–15% smoke suppressant, 5%–8% other additives, and 0.5%–2% graphene oxide; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

11. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 1 or 10, characterized in that, The flame retardant and flame retardant additive are flame retardants and flame retardant additives that have been pre-blended with phenolic resin or acrylic resin.

12. A low-smoke, self-extinguishing, flame-retardant optical cable, comprising a cable core and a sheathing layer covering the cable core, characterized in that, The protective layer comprises an outer protective layer and an inner protective layer; the outer and inner protective layers employ two different low-smoke flame-retardant materials, wherein the first low-smoke flame-retardant material of the outer protective layer has a maximum specific optical density of 25–55 during flaming combustion, and the second low-smoke flame-retardant material of the inner protective layer has a maximum specific optical density of 125–250 during flameless combustion; The first low-smoke flame-retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 5%–8% halogenated aromatic polymer resin, 15%–25% flame retardant, 5%–10% flame retardant additive, 5%–8% smoke suppressant, and 5%–8% other additives; the halogenated aromatic polymer resin is a bromine-containing aromatic polymer; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

13. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 12, characterized in that, The second low-smoke flame-retardant material comprises the following components by weight percentage: 35%–45% polyolefin base resin, 15%–25% flame retardant, 5%–8% flame retardant additive, 8%–15% smoke suppressant, 5%–8% other additives, and 0.5%–2% graphene oxide; the flame retardant is at least one of magnesium hydroxide and aluminum hydroxide; the flame retardant additive is at least one of red phosphorus, carbon black, organosilicon, antimony trioxide, and magnesium borate; the smoke suppressant is a molybdenum-containing compound; and the other additives include at least one of compatibilizer, antioxidant, ultraviolet absorber, and heat stabilizer.

14. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 12 or 13, characterized in that, The flame retardant and flame retardant additive are flame retardants and flame retardant additives that have been pre-blended with phenolic resin or acrylic resin.

15. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 12, characterized in that, The coating layer comprises, from the outside to the inside, an outer protective layer, a non-metallic fiber layer, a smoking layer, an inner protective layer, and a water-blocking layer; the smoking layer comprises two graphene films and activated carbon particles located between the two graphene films.

16. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 15, characterized in that, The non-metallic fiber layer is woven from multiple strands of non-metallic fibers, and there are at least two layers of non-metallic fiber layer, forming a honeycomb structure.

17. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 15, characterized in that, The activated carbon particles are ultrafine activated carbon particles with a particle size of 0.5 μm to 20 μm.

18. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 12, characterized in that, The cable core includes a fire extinguishing unit, a steel strip, an optical unit, and a central reinforcement unit. The central reinforcement unit is located at the center of the optical cable and extends along the length of the optical cable. The optical units are twisted around the periphery of the central reinforcement unit. The steel strip is a single unit along the circumference of the optical cable, covering the periphery of all the optical units. The outer periphery of the steel strip forms spaced concave and convex surfaces. The fire extinguishing unit is filled in the concave surface of the steel strip.

19. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 18, characterized in that, The outer surface of the steel strip between two adjacent optical units forms a concave surface, and the outer surface of the steel strip at the optical unit forms a convex surface; there are multiple fire extinguishing units in the concave surface, the fire extinguishing unit at the deepest part of the concave surface has the largest volume, and the volumes of the fire extinguishing units on both sides of the deepest part of the concave surface along the circumferential direction of the cable core decrease sequentially.

20. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 18, characterized in that, The height of the concave surface after the fire extinguishing unit is filled is higher than that of the convex surface, and the wall thickness of the inner protective layer near the convex surface is greater than that of the inner protective layer near the concave surface.

21. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 18, characterized in that, The steel strip is longitudinally wrapped without overlapping, and the two sides are aligned and welded to form a closed cavity.

22. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 18, characterized in that, The fire extinguishing unit is covered with a thin-walled plastic layer and filled with fire extinguishing agent.

23. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 22, characterized in that, The extinguishing agent is at least one of the following: a mixture of flame-retardant ultrafine solid powders with a particle size ≤0.5μm, a nano-substrate composite metal oxide, an inert gas, or a non-flammable gas.

24. A low-smoke, self-extinguishing, flame-retardant optical cable according to claim 18, characterized in that, The optical unit comprises, from the outside to the inside, a first plastic layer, a fire-resistant layer, a second plastic layer, a water-blocking material, and an optical fiber. The heat distortion temperature, thermal decomposition temperature, and melting point of the first plastic layer are all greater than those of the second plastic layer. The fire-resistant layer is a polyimide composite tape coated with mica powder. The first plastic layer, the fire-resistant layer, and the second plastic layer are formed by co-extrusion of three layers simultaneously. The water-blocking material is water-blocking yarn.

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