A high flame-retardant hollow core fiber optical cable with gradient heat insulation and self-ignition fire extinguishing mechanism

Abstract

The application belongs to the field of optical communication transmission technology, and discloses a high-flame-retardant hollow-core optical fiber cable with gradient heat insulation and self-ignition fire extinguishing mechanism, which comprises, from inside to outside, a hollow-core optical fiber unit, an aerogel heat insulation buffer layer, a microcapsule phase change heat absorption layer, a self-expanding ceramicized flame-retardant layer and an outer sheath layer, wherein the overall structure is redesigned, and the specific structure and processing method of some key components are improved, so that the gradient collaborative mechanism of "reflective heat insulation + phase change heat absorption + expansion carbonization" can be reasonably utilized, the safety threshold of the telecommunication equipment can be ensured under high-temperature environment, and higher fire resistance integrity can be achieved; in addition, compared with the prior art, the problem of heat convection sensitivity of the hollow-core optical fiber caused by the internal hollow is effectively solved, the phase stability of the optical transmission path in the fiber core is ensured, and the critical temperature in the hollow-core optical fiber cable can be more conveniently controlled.

Description

Technical Field

[0001] This invention belongs to the field of optical communication transmission technology, and more specifically, relates to a highly flame-retardant hollow optical fiber cable with a gradient heat insulation and self-extinguishing fire mechanism. Background Technology

[0002] With the exponential growth of communication capacity, hollow-core optical fiber, due to its low latency, low nonlinearity, and low dispersion characteristics, is regarded as the core medium for next-generation optical communication. However, existing hollow-core optical fiber cables face severe challenges in fire resistance and flame retardancy during commercialization.

[0003] To provide the required fire-retardant performance, existing flame-retardant optical cables mainly adopt the following solutions: one is to configure a passive fire-resistant layer, such as using ceramicized polyolefin or mica tape to form a hard shell at high temperatures to resist flame burning; the other is to configure a heat insulation structure, such as using glass fiber or asbestos materials for thermal insulation.

[0004] However, further research shows that when conventional flame-retardant solutions are applied to the specific application of hollow-core optical fiber cables, the following technical challenges remain: First, existing technologies do not adequately consider blocking "axial thermal convection." Existing solid glass optical fibers have a dense core material, resulting in slow heat conduction. Hollow-core optical fibers, on the other hand, have an air core (or inert gas) inside. Although a glass cladding exists, during a fire, high external temperatures can easily penetrate into the fiber core through thermal radiation and air convection. In this situation, once the core temperature exceeds a threshold, the gas refractive index distribution changes, and communication will be instantly interrupted.

[0005] Secondly, existing technologies suffer from a disconnect between heat insulation and flame retardancy. Current hollow-core optical fiber cables typically use multiple overlapping flame-retardant layers (low-smoke halogen-free LSZH). While these materials are inherently flame-retardant, they have high thermal conductivity (>0.2 W / m·K). Under high-temperature flames such as >800℃, heat will rapidly pass through the sheath and be conducted to the interior, like a sponge absorbing water, causing the hollow fiber coating to soften and collapse.

[0006] Third, existing technologies exhibit delayed failure. While existing hollow-core optical fibers can maintain their integrity for several minutes when directly sprayed with flame, once the heat accumulation reaches the material's tolerance limit, the internal temperature spikes instantly (thermal collapse effect). Therefore, there is a lack of mechanisms to actively suppress internal temperature rise.

[0007] Accordingly, it is necessary to conduct further research and improvements in this field in order to better address the aforementioned technical pain points. Summary of the Invention

[0008] To address one or more of the above-mentioned defects or improvement needs of existing technologies, this invention provides a high flame-retardant hollow fiber optic cable with a gradient heat insulation and self-ignition fire extinguishing mechanism. The overall structure of the hollow fiber optic cable is redesigned by fully addressing the aforementioned technical pain points, and targeted improvements are made to the specific structures and processing methods of key components such as the aerogel heat insulation buffer layer, the microcapsule phase change heat absorption layer, and the self-expanding ceramic flame-retardant layer. This allows for the rational utilization of the gradient synergistic mechanism of "reflective heat insulation + phase change heat absorption + expansion carbonization," ensuring that the hollow fiber optic cable maintains the safety threshold of telecommunications-grade equipment even in high-temperature environments and achieves higher fire resistance integrity. At the same time, compared with existing technologies, it effectively solves the problem of heat convection sensitivity caused by the hollow interior of hollow optical fibers, ensuring the phase stability of the optical transmission path inside the fiber core. In addition, it can more conveniently and actively control the critical temperature inside the hollow optical fiber cable. Therefore, it is particularly suitable for high flame-retardant hollow optical fiber cable application scenarios with extremely high fire safety requirements, such as data centers, rail transit, ships and high-rise buildings.

[0009] To achieve the above objectives, according to the present invention, a high flame-retardant hollow optical fiber cable with a gradient heat insulation and self-ignition fire extinguishing mechanism is provided. This high flame-retardant hollow optical fiber cable comprises, from the inside out, a hollow optical fiber unit, an aerogel heat insulation buffer layer, a microcapsule phase change heat absorption layer, a self-expanding ceramic flame-retardant layer, and a low-smoke halogen-free outer sheath layer, wherein: The hollow fiber unit includes a hollow fiber and an inner sleeve. The hollow fiber is placed in the inner sleeve and filled with nitrogen. The aerogel thermal insulation buffer layer uses nanoporous aerogel as the substrate to block external heat from being conducted into the solid state of the hollow optical fiber unit. The microcapsule phase change heat absorption layer undergoes a phase change and absorbs heat after the external temperature reaches a preset value, which is used to actively absorb heat that seeps in from the outside. The self-expanding ceramic flame-retardant layer is premixed from multiple components, which, by weight, include: polyolefin base material, 40 to 60 parts; ceramic powder, 25 to 40 parts; and expandable graphite, 10 to 20 parts. In addition, during the preparation of the aerogel heat insulation buffer layer, the microcapsule phase change heat absorption layer, and the self-expanding ceramic flame retardant layer, nitrogen gas is continuously introduced into the inner sleeve and kept at positive pressure to ensure that the hollow optical fiber is always in an unpressurized state.

[0010] As a further preferred embodiment of the present invention, the hollow fiber unit adopts an anti-resonant type or a photonic bandgap type hollow fiber with an air core; in addition, the outer surface of the hollow fiber needs to be stripped of the original acrylate coating layer and then uniformly coated with a polyimide coating or a silicone resin coating.

[0011] As a further preferred embodiment of the present invention, for the hollow optical fiber unit, the hollow optical fiber is in a free and loose state with a gap of 0.1 mm to 0.2 mm in the inner sleeve; the outer side of the inner sleeve is preferably also wrapped with non-woven fabric or water-blocking yarn to absorb any moisture that may seep in and to assist in buffering.

[0012] As a further preferred embodiment of the present invention, the inner sleeve is prepared by an extrusion process, and during the extrusion process, positive pressure dry nitrogen gas of 0.01MPa to 0.03MPa is preferably introduced into the channel between the extruder head and the hollow optical fiber.

[0013] As a further preferred embodiment of the present invention, the aerogel thermal insulation buffer layer preferably uses nanoporous silica aerogel as the substrate, and the relevant key parameters are set as follows: Aerogel pore size: 25nm~50nm; aerogel mass fraction: 15%~30%; thickness of aerogel thermal insulation buffer layer: 1.0mm~2.0mm; aerogel porosity retention rate: ≥85%; temperature gradient with adjacent interface: ≥200℃ / mm.

[0014] As a further preferred embodiment of the present invention, the microcapsule phase change heat-absorbing layer comprises a plurality of microcapsules dispersed in a flexible substrate, each microcapsule using a phase change material such as paraffin and salt as the core and a thermosetting polymer such as melamine-formaldehyde resin as the outer shell; the flexible substrate is preferably made of silicone rubber.

[0015] As a further preferred embodiment of the present invention, the self-expanding ceramic flame-retardant layer preferably further comprises the following additives, by weight: Silane coupling agent, 1 to 2 parts; antioxidant, 0.5 to 1 part; lubricant, 1 to 2 parts.

[0016] As a further preferred embodiment of the present invention, the self-expanding ceramic flame-retardant layer is preferably prepared by the following process steps: Ingredients and dry mixing: Weigh each component according to the set ingredient ratio, premix the ceramic powder and the expandable graphite in a high-speed mixer for 3 to 5 minutes, then add the silane coupling agent and continue mixing for more than 5 minutes to obtain a dry mixture and modify the surface of the powder. Twin-screw compounding: The above dry mixture and the polyolefin base material are fed into a co-rotating twin-screw extruder for melt compounding. The relevant process parameters are as follows: screw length-to-diameter ratio: 44:1 to 52:1; screw speed: 250 rpm to 350 rpm. Vacuum exhaust: Turn on the vacuum pump in the exhaust section, with a vacuum degree ≤ –0.06MPa, to remove moisture and low molecular weight volatiles; Granulation and drying: The uniformly mixed material is granulated and dried at 80℃~100℃ for more than 4 hours to ensure that the moisture content is ≤0.1% and to avoid the generation of air bubbles during extrusion.

[0017] As a further preferred embodiment of the present invention, the aerogel heat insulation buffer layer, the microcapsule phase change heat absorption layer, and the self-expanding ceramic flame retardant layer are preferably multi-layered and coated in one step through a co-extrusion process.

[0018] As a further preferred embodiment of the present invention, the low-smoke halogen-free outer sheath layer preferably adopts a double-layer design, wherein the inner layer is made of polyolefin oxygen barrier material, and the outer layer is made of ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer as matrix resin, and magnesium hydroxide is used as the main flame retardant. It also contains a variety of synergistic flame retardants, namely fibrous hydrous magnesium silicate, silicate natural minerals, and polyolefin NP flame retardant.

[0019] In summary, the technical solutions conceived by this invention have the following main technical advantages compared with the prior art: (1) The core improvement of this invention lies first in the redesign of the internal structure and overall flame retardant mechanism of the high flame retardant optical fiber cable; in which the aerogel heat insulation buffer layer is set, its nano-sized pores can effectively restrict the thermal movement of gas molecules, thus serving as the first barrier to block heat conduction and effectively blocking the external heat to the solid conduction inside the hollow optical fiber. Building upon this foundation, the present invention further incorporates a microcapsule phase change heat-absorbing layer. When the fire temperature reaches a preset value (i.e., a temperature threshold, such as 60°C to 90°C), it immediately undergoes a phase change and absorbs a large amount of heat during this phase change process, while maintaining its own temperature. This layer is specifically designed to absorb heat penetrating from the outside, thereby protecting the temperature field of the hollow optical fiber. Simultaneously, the present invention also incorporates a self-expanding ceramic flame-retardant layer. Upon exposure to high temperatures, this layer rapidly expands in volume (up to 100 to 300 times its original volume), compressing and extinguishing any possible gap flames. This forms a dense carbon skeleton structure that tightly encapsulates the interior, preventing oxygen penetration and reflecting some of the heat radiation. (2) Through the redesign of the above internal structure and overall flame-retardant mechanism, the present invention can perform the following specific working process: In the first stage, also known as the initial fire, at approximately 200℃-400℃: the low-smoke halogen-free outer sheath quickly forms a ceramic shell upon contact with the fire, isolating it from direct external oxygen erosion. At the same time, the internal microcapsule phase change heat-absorbing layer begins to activate, absorbing the infiltrated heat through melting to ensure that the microenvironment temperature of the hollow optical fiber does not rise suddenly. The second stage, also known as the mid-stage fire, occurs at approximately 400°C to 800°C: If heat continues to penetrate, the self-expanding ceramic flame-retardant layer is activated, and the expanded graphite expands and compacts, forming a thicker heat insulation barrier. The third stage, also known as extreme fire, at temperatures above 800°C, involves the complete sintering of the self-expanding ceramic flame-retardant layer into a hard shell, providing a certain degree of resistance to mechanical impact. At this stage, the inner aerogel insulation buffer layer utilizes its extremely low thermal conductivity to prevent the final heat radiation and conduction from entering the hollow optical fiber.

[0020] The three components achieve a "heat sink gradient" through a gradual decrease in heat flow gradient: external temperature 1000℃ → expansion ceramic layer reduces the temperature to about 300℃ → phase change layer absorbs heat and maintains about 80℃ → aerogel layer insulates and buffers → hollow optical fiber operates within the maximum range, thus achieving the required flame retardant effect. (3) By combining the latent heat absorption of phase change materials with the thermal insulation of aerogel, this invention can achieve an ultra-high fire resistance time compared with the prior art. The fire resistance time is extended from the conventional 30-90 minutes to more than 180 minutes, meeting the requirements of special fire protection levels. At the same time, it effectively solves the problem of heat convection sensitivity caused by the hollow interior of hollow optical fiber, and ensures the phase stability of the optical transmission path inside the fiber core; in addition, the microcapsule phase change heat absorption layer in this invention actively absorbs heat, which can more effectively control the critical temperature inside the optical cable. (4) The present invention further improves the specific structure and material selection of the low-smoke halogen-free outer sheath layer. The resulting hollow fiber optic cable is a full-dielectric (metal-free) design, which avoids the bulkiness and inconvenience of metal sheaths. Moreover, the flame-retardant material burns with low smoke and non-toxicity (LSZH characteristics), thus better meeting the requirements of environmental protection and lightweighting. It is especially suitable for high flame-retardant hollow fiber optic cable application scenarios with extremely high fire safety requirements, such as data centers, rail transit, ships and high-rise buildings. Attached Figure Description

[0021] Figure 1 This is a cross-sectional view of the overall structural composition of a high flame-retardant hollow optical fiber cable with a gradient heat insulation and self-ignition fire extinguishing mechanism designed according to the present invention. In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1- Hollow fiber unit; 2- Aerogel thermal insulation buffer layer; 3- Microcapsule phase change heat absorption layer; 4- Self-expanding ceramic flame retardant layer; 5- Low smoke halogen-free outer sheath layer; 101- Hollow fiber; 102- Inner sheath. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

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

[0025] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0027] Figure 1 This is a cross-sectional view of the overall structure of a high flame-retardant hollow optical fiber cable with a gradient heat insulation and self-extinguishing fire mechanism designed according to the present invention. The following will refer to... Figure 1 To explain the invention in more detail.

[0028] like Figure 1 As demonstrated in the present invention, the high flame-retardant hollow optical fiber cable designed according to the present invention is firstly designed in layers from the perspective of its structural composition. From the inside out, it mainly includes a hollow optical fiber unit 1, an aerogel thermal insulation buffer layer 2, a microcapsule phase change heat absorption layer 3, a self-expanding ceramic flame-retardant layer 4, and a low-smoke halogen-free outer sheath layer 5, wherein: The hollow fiber unit includes a hollow fiber 101 and an inner sleeve 102. The hollow fiber 101 is placed in the inner sleeve 102 and filled with nitrogen. The aerogel thermal insulation buffer layer uses nanoporous aerogel as the substrate to block external heat from being conducted into the solid state of the hollow optical fiber unit. The microcapsule phase change heat absorption layer undergoes a phase change and absorbs heat after the external temperature reaches a preset value, which is used to actively absorb heat that seeps in from the outside. The self-expanding ceramic flame-retardant layer is premixed from multiple components, which, by weight, include: polyolefin base material, 40 to 60 parts; ceramic powder, 25 to 40 parts; and expandable graphite, 10 to 20 parts. In addition, the aerogel heat insulation buffer layer, the microcapsule phase change heat absorption layer, and the self-expanding ceramic flame retardant layer are coated in multiple layers in one go through a co-extrusion process. During this co-extrusion process, nitrogen gas is continuously introduced into the inner sleeve and kept at positive pressure to ensure that the hollow optical fiber is always in an unpressurized state.

[0029] Through the above design, firstly, the nanoscale pores of the aerogel thermal insulation buffer layer can effectively restrict the thermal movement of gas molecules, thus acting as the first barrier to block heat conduction and effectively blocking the solid-state conduction of external heat into the hollow fiber. On this basis, on the one hand, due to the specially designed microcapsule phase change heat absorption layer, it will immediately undergo a phase change when the fire temperature reaches the preset temperature threshold (e.g., 60℃~90℃), and absorb a large amount of heat during this phase change process while maintaining its own temperature. This is specifically used to absorb heat that penetrates from the outside, thereby protecting the temperature field of the hollow fiber. On the other hand, due to the specially designed self-expanding ceramic flame retardant layer, it will rapidly expand in volume (up to 100 to 300 times its original volume) when exposed to high temperatures, squeezing and extinguishing any possible gap flames, thereby forming a dense carbon skeleton structure that tightly wraps the interior, preventing oxygen from penetrating and reflecting some heat radiation. Accordingly, the present invention can obtain a gradient synergistic mechanism of "reflective heat insulation + phase change heat absorption + expansion carbonization", thereby ensuring that hollow fiber optic cables can still maintain the safety threshold of telecommunications equipment in high-temperature environments and achieve higher fire resistance integrity. In particular, compared with the prior art, the above-mentioned synergistic mechanism of the present invention also effectively solves the problem of heat convection sensitivity caused by the hollow interior of hollow fiber, ensures the phase stability of the optical transmission path inside the fiber core, and can also more conveniently and actively control the critical temperature inside the hollow fiber optic cable.

[0030] After summarizing the overall structural components of the present invention and its flame-retardant synergistic mechanism, the following will provide a more detailed explanation of each of the above components.

[0031] (a) Hollow-core fiber unit For hollow fiber unit 1, its hollow fiber can be, for example, an anti-resonant type or a photonic bandgap type hollow fiber, with air as the core; in addition, according to a preferred embodiment of the present invention, the outer surface of the hollow fiber 101 needs to be stripped of the original acrylate coating layer, and then uniformly coated with a polyimide coating or a silicone coating; accordingly, a higher temperature resistance (≥400°C) can be obtained.

[0032] According to a preferred embodiment of the present invention, the specific processing procedure for the hollow optical fiber unit 1 is as follows: (a) Preprocessing of hollow fiber 101 Step 1: Remove the original coating. The hollow optical fiber is completely stripped of the acrylic coating by passing it through a hot acetone steam cleaning tank (temperature controlled at 60±5℃) or a laser wire stripping device, exposing the glass cladding surface.

[0033] Step 2: Coating with high-temperature resistant material. A cavity-type precision coating mold is used to uniformly coat a layer of polyimide or high-temperature resistant silicone resin onto the surface of the bare optical fiber.

[0034] Polyimide coating process: Using a polyamic acid precursor solution, the coating is passed through a five-stage thermal imidization furnace (furnace temperatures sequentially: 80℃→150℃→250℃→350℃→200℃) to form a 10-15μm thick polyimide coating on the optical fiber surface. This coating can withstand temperatures ≥400℃ and exhibits good adhesion to the glass cladding.

[0035] High-temperature resistant silicone resin coating process: UV-curable silicone resin is used. After coating, it is quickly cured by a UV lamp (wavelength 365nm, light intensity 800mW / cm²) with the thickness controlled at 15-20μm.

[0036] (b) Formation of inner sleeve 102 Step 1: First extrusion – forming the inner buffer sleeve; Its processing equipment can be equipped with a micro-pressure screw extruder (screw diameter Φ25mm, length-to-diameter ratio 25:1), with a vacuum sizing groove and a pressure-balanced extruder head.

[0037] Materials can be low-modulus, high-flexibility thermoplastic elastomers, such as thermoplastic polyurethane (TPU, hardness 65A) or styrene-based thermoplastic elastomers (SEBS).

[0038] The corresponding key process parameters are as follows: Temperatures of each section of the extruder: feeding section 150℃ → plasticizing section 170℃ → homogenizing section 180℃ → die head 185℃.

[0039] Key control point: Pressure balance within the extruder head. A positive pressure of 0.01-0.03 MPa of dry nitrogen is introduced into the channel between the extruder head and the hollow optical fiber. This positive pressure serves two purposes: firstly, it prevents the molten plastic from collapsing due to gravity or uneven pressure, directly contacting and compressing the hollow optical fiber; secondly, it forms an extremely thin air cushion layer between the optical fiber and the molten plastic, allowing the plastic to flow uniformly around the optical fiber.

[0040] Extrusion speed: 5-10 m / min (low speed to avoid vibration).

[0041] Cooling method: After extrusion, the material is immediately passed through a 30℃ warm water bath for gentle cooling to avoid excessive internal stress caused by rapid cooling.

[0042] Output: An inner sheath (thickness 0.3-0.5mm) is formed, in which the hollow optical fiber is in a free and loose state (gap of about 0.1-0.2mm), and the internal nitrogen atmosphere provides a certain degree of inert protection for flame retardancy.

[0043] Step 2: Apply water-blocking / heat-insulating materials at intervals Outside the inner sleeve 102, a thin layer of non-woven fabric or water-resistant yarn can be wrapped around it using a non-contact wrapping machine (to absorb any moisture that may seep in and to provide additional cushioning).

[0044] (ii) Pre-integration of the outer functional layer (aerogel thermal insulation buffer layer 2 + microcapsule phase change heat absorption layer 3 + self-expanding ceramic flame retardant layer 4) On the outside of the already manufactured inner sheath + hollow fiber assembly, multiple functional layers can preferably be coated in one step using a co-extrusion die. A tandem co-extrusion production line is recommended for this step. First co-extrusion layer: Aerogel-silicone rubber composite layer. Silica aerogel powder (particle size 10-50μm, 15-25% by mass) is thoroughly mixed with liquid addition-type silicone rubber and fed into the extruder head via a metering pump to form an aerogel insulation layer with a thickness of 1.0-1.5mm on the outside of the sleeve. After extrusion, it is cured through an 80℃ hot air channel.

[0045] Second co-extruded layer: Phase change silicone rubber layer. Before the aerogel layer is fully cured (the surface is still sticky), a silicone rubber layer containing microcapsule phase change material with a thickness of 1.5-2.0 mm is superimposed on the outside using a second extruder.

[0046] Note: During the co-extrusion process, nitrogen gas must be continuously supplied to the inner sleeve under positive pressure until the entire extrusion-cooling section is completed, to ensure that the hollow fiber is always in an unpressurized state.

[0047] (III) As one of the key components of this invention, the aerogel thermal insulation buffer layer 2 serves as the first barrier to block heat conduction. Its working mechanism is as follows: the nanoscale pores of the aerogel restrict the thermal movement of gas molecules, effectively blocking the solid-state conduction of external heat to the interior of the hollow optical fiber.

[0048] More specifically, according to another preferred embodiment of the present invention, the aerogel thermal insulation buffer layer 2 preferably uses nanoporous silica aerogel as the substrate, wherein the pure silica aerogel powder / particle morphology is selected as follows: hydrophobic silica aerogel micropowder with an average particle size of 20–80 μm, a pore size distribution of 20–50 nm, a porosity ≥90%, and a thermal conductivity ≤0.020 W / m·K. Before use, it needs to be dried in a vacuum drying oven at 80℃-100℃ for 12 hours to remove adsorbed moisture and avoid the generation of bubbles or interference with curing during subsequent mixing with the silicone rubber matrix.

[0049] More specifically, according to another preferred embodiment of the present invention, the aerogel thermal insulation buffer layer 2 can be processed by a fiber-reinforced aerogel felt wrapping / longitudinal wrapping method, and the specific process steps are as follows: Unwinding and width cutting: The rolled fiber-reinforced aerogel felt is cut into strips with a width of 5–15 mm using a precision slitting machine (the specific width depends on the core diameter and overlap requirements).

[0050] Application of wrapping: Use a double-headed or triple-headed wrapping machine, with the wrapping speed and cable core traction speed linked for control. Wrap the aerogel felt strip spirally around the outer surface of the inner sheath (including hollow optical fiber) with an overlap rate of 30%–50%. The recommended wrapping angle is 45°–60°, and the wrapping tension is controlled at 2–5N (depending on the tensile strength of the aerogel felt; fiber-reinforced types can withstand higher tensions). Alternatively, a longitudinal wrapping method can be used: For optical cables with more regular structures, the aerogel felt can be directly wrapped longitudinally around the cable core, with an overlap of 5–10mm at the joint, and temporarily fixed with hot melt adhesive tape or polyester tape.

[0051] Compaction and shaping: After wrapping / longitudinally wrapping, the cable core is passed through a set of sizing molds (the aperture is slightly larger than the outer diameter of the cable core by 0.1–0.3 mm) to evenly compress the aerogel felt, expel interlayer air, and ensure consistent thickness.

[0052] According to another preferred embodiment of the present invention, in order to ensure that the aerogel layer truly utilizes the physical mechanism of nanopore-confined heat conduction, the following key parameters are preferably strictly defined as shown in Table 1:

[0053] Table 1 More specifically, according to another preferred embodiment of the present invention, for the bonding of the aerogel thermal insulation buffer layer 2 and the inner layer (hollow fiber inner sleeve), before the construction of the aerogel thermal insulation buffer layer 2, the surface of the inner sleeve is preferably subjected to plasma surface treatment (power 300W, treatment time 3-5 seconds) to improve the adhesion of subsequent coatings or wrapping layers and avoid interlayer peeling under high temperature conditions.

[0054] More specifically, according to another preferred embodiment of the present invention, for the bonding of the aerogel heat insulation buffer layer 2 with the outer layer (phase change heat absorption layer or flame retardant layer), it is preferable to wrap a thin polyester binding tape (thickness ≤ 0.05 mm, overlap rate 20%) around the aerogel felt to fix the felt and provide a smooth surface for subsequent layer construction operations.

[0055] The quality inspection method for aerogel thermal insulation buffer layer 2 is as follows: Thermal conductivity test: A sample of the aerogel layer was taken and tested at room temperature and 300℃ using a thermal conductivity meter (ASTM D5470 standard) to verify that its thermal conductivity is ≤0.025 W / m·K.

[0056] Thickness uniformity: Take a cross section every meter along the optical cable axis and measure the thickness of the aerogel layer at four orthogonal points on the circumference under a microscope. The deviation is ≤ ±0.1 mm.

[0057] Interface bonding strength: A 90° peel test is conducted, and the peel force between the aerogel layer and the adjacent layer should be ≥0.5 N / cm to ensure that the layers do not delaminate under high temperatures in a fire.

[0058] (iv) As another key component of the present invention, the microcapsule phase change heat absorption layer 3 preferably includes microcapsules with paraffin or hydrated salt phase change material as the core and thermosetting polymer (such as melamine-formaldehyde resin) as the outer shell, and dispersed in a flexible silicone rubber matrix.

[0059] Its mechanism of action is based on the principle of "latent heat of phase change" for active thermal management. More specifically, when the fire temperature reaches 60℃-90℃, the phase change material begins to melt. During this phase change process, it absorbs a large amount of heat (high energy density) while its own temperature remains constant. This is similar to installing a "heat sponge" inside an optical cable, specifically designed to absorb heat that seeps in from the outside, thereby protecting the temperature field stability of the hollow optical fiber.

[0060] (v) As another key component of the present invention, the self-expanding ceramic flame-retardant layer 4 is mainly composed of ceramic powder (wollastonite, mica, etc.) and high-temperature expanded graphite added to EVA or polyolefin base material. Its function is to provide physical insulation and thermal insulation barrier construction.

[0061] More specifically, the working mechanism of the self-expanding ceramic flame-retardant layer 4 can be explained as follows: When exposed to high temperatures (>300℃), the expanded graphite rapidly expands in volume (up to 100-300 times its original volume), compressing and extinguishing any possible void flames, forming a dense carbon skeleton structure similar to "ceramic armor". This layer tightly wraps the interior, preventing oxygen from penetrating and reflecting some of the heat radiation.

[0062] More specifically, the overall preparation process of the self-expanding ceramic flame-retardant layer 4 is as follows: (a) Material composition and premixing The base material system of this self-expanding ceramicized flame-retardant layer is an intumescent ceramicized polyolefin composite material, which, according to a specific embodiment of the present invention, can be composed of the specific components shown in Table 2 below in parts by mass:

[0063] Table 2 (b) Premixing and granulation process steps: Ingredients and dry mixing: Weigh each component according to the above proportions. First, premix the ceramic powder and expandable graphite in a high-speed mixer for 3-5 minutes. Then, add the silane coupling agent and continue mixing for 5 minutes to modify the surface of the inorganic powder and improve its compatibility with polyolefin base materials.

[0064] Twin-screw compounding: The dry mix and polyolefin base material are fed into a co-rotating twin-screw extruder for melt compounding. The specific process parameters are as follows: Screw length-to-diameter ratio: 44:1–52:1 (to ensure adequate packing dispersion); Temperature settings: Feeding section 140℃ → Melting section 160℃ → Mixing section 170℃ → Exhausting section 165℃ → Die head 170℃; Screw speed: 250–350 rpm; Vacuum exhaust: Turn on the vacuum pump in the exhaust section, with a vacuum degree ≤ –0.06MPa, to remove moisture and low molecular weight volatiles; Granulation and Drying: The uniformly mixed material is processed into cylindrical pellets (2-3 mm in diameter and 3-4 mm in length) using a water-cooled string pelletizing or underwater pelletizing system. The pellets are then dried in an 80℃ circulating hot air drying oven for 4 hours to ensure a moisture content of ≤0.1% and to prevent air bubbles from forming during extrusion.

[0065] (c) The molding steps of the self-expanding ceramic flame retardant layer.

[0066] According to the design requirements of optical cable structure, the self-expanding ceramic flame retardant layer can be formed by extrusion coating or wrapping molding, with extrusion coating preferred to achieve structural consistency with continuous interlayer and no air gap.

[0067] Preferred process: Single-screw extrusion coating method Equipment configuration: A high compression ratio single-screw extruder (screw diameter Φ45mm, length-to-diameter ratio 25:1, compression ratio 3.5:1) is used, paired with a semi-extrusion die head or a tubular die head. The semi-extrusion die head allows the melt to uniformly coat the cable core surface under lower pressure, reducing compression damage to the internal aerogel layer and hollow optical fiber.

[0068] More specifically, according to a preferred embodiment of the present invention, the relevant extrusion process parameters are shown in Table 3:

[0069] Table 3 Key control point: Preventing pre-expansion during extrusion. Accordingly, the initial expansion temperature of expandable graphite is approximately 220–250°C, and theoretically, no significant expansion will occur when extruded at 170°C. However, it is important to note that: Local hot spots inside the extruder (such as the screw shearing zone) must not exceed 200°C; if the machine is stopped for more than 15 minutes, the residual material in the barrel must be discharged to avoid the material remaining for a long time, which may cause the graphite part to expand and block the die head.

[0070] Auxiliary / alternative process: Ceramicized flame-retardant tape wrapping method (for thick or multi-layer structures) When the total thickness of the flame-retardant layer required by the design exceeds 2.0 mm, the inner layer (0.5–0.8 mm) can be first coated by extrusion, and then a pre-fabricated ceramic flame-retardant strip can be wrapped around the outside. Flame retardant tape specifications: Use commercially available ceramicized silicone rubber tape or ceramicized polyolefin tape, with a thickness of 0.2–0.3 mm and a width of 15–30 mm.

[0071] More specifically, according to another preferred embodiment of the present invention, the relevant wrapping parameters are as follows: The speed of the wrapping machine is linked to the traction speed to ensure an overlap rate of 50%–60% (i.e., more than half of the overlap is between two wraps).

[0072] The wrapping tension should be 3–6 N. Excessive tension may damage the internal aerogel layer.

[0073] The wrapping angle is 30°–45°, forming a cross-wound structure to enhance radial compressive strength.

[0074] (d) Cooling and shaping of the self-expanding ceramic flame-retardant layer The extruded self-expanding ceramic flame-retardant layer must undergo staged cooling to avoid internal stress and surface defects. First cooling section (rapid shaping): The outer surface is rapidly cooled to below 80°C through a 1.5m long 10°C circulating water tank, forming a smooth skin.

[0075] Second cooling stage (slow cooling): The core temperature is then slowly reduced to ambient temperature by passing through a 3m long room temperature water bath (approximately 25℃).

[0076] Drying: After cooling, the surface water stains are dried by high-pressure air knife (wind speed 20–30 m / s) to avoid the introduction of moisture in subsequent processes.

[0077] (e) The quality inspection and performance verification methods are shown in Table 4 below:

[0078] Table 4 More specifically, according to another preferred embodiment of the present invention, the process connection requirements between the self-expanding ceramic flame-retardant layer and the adjacent layer are as follows: For the bonding with the microcapsule phase change heat-absorbing layer: Before extruding the self-expanding ceramic flame-retardant layer, the surface of the phase change heat-absorbing layer should be clean, dry, and free of oil. If the surface of the phase change layer has been completely cured, corona treatment (power 1.5kW, processing speed 10m / min) is required to increase the surface energy and ensure that the interfacial bonding force between the flame-retardant layer and the phase change layer is ≥0.8 N / cm.

[0079] (vi) As another key component of the present invention, the low-smoke halogen-free outer sheath layer 5 is preferably designed with a double layer, wherein the inner layer is made of polyolefin oxygen barrier material, and the outer layer is made of ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer as the matrix resin, and magnesium hydroxide is used as the main flame retardant. It also contains a variety of synergistic flame retardants, namely fibrous hydrous magnesium silicate, silicate natural minerals, and polyolefin NP flame retardant.

[0080] More specifically, according to a specific embodiment of the present invention, the outer layer comprises the following main raw materials: Ethylene-vinyl acetate copolymer (EVA1828, VA content 28%), Hanwha Chemical Materials Co., Ltd. Ethylene-vinyl acetate copolymer (EVA 180, VA content 33%), Mitsui Dow Chemical Co., Ltd. Ethylene-octene copolymer C1070D, SABIC; Metallocene polyethylene: SP1520, Prima Polymers, Inc. Compatibilizer: M206-H, manufactured in-house by CGN High-Tech Nuclear Materials (Jiangsu) Co., Ltd. Inorganic flame retardant: Magnesium hydroxide (MH, particle size D50≈1.0μm), industrial grade; Synergistic flame retardant A: fibrous hydrated magnesium silicate, industrial grade; Synergistic flame retardant B: a natural silicate mineral, industrial grade; A novel polyolefin NP flame retardant, industrial grade.

[0081] Processing aids: silane coupling agent, antioxidant (1010 / DLTP / 1076 composite), lubricant (zinc stearate, silicone masterbatch, PE wax), all of which are industrial grade.

[0082] Related experimental test results show that when magnesium hydroxide, an inorganic flame retardant, is used as the main flame retardant, and flame retardant synergist A, flame retardant synergist B, and NP flame retardant are used as the synergistic system, the prepared low-smoke halogen-free flame-retardant polyolefin cable material can achieve a limiting oxygen index (LOI) of 44%, pass the FV-0 level in vertical combustion, has low smoke density, and maintains good mechanical properties and extrusion processing performance, fully meeting the stringent requirements for B1 grade cable materials in GB 31247-2014 standard.

[0083] The working process of the high flame-retardant hollow optical fiber cable of the present invention when it encounters a fire will be explained in more detail below.

[0084] In the first stage, also known as the initial fire, at approximately 200℃-400℃: the low-smoke halogen-free outer sheath quickly forms a ceramic shell upon contact with the fire, isolating it from direct external oxygen erosion. At the same time, the internal microcapsule phase change heat-absorbing layer begins to activate, absorbing the infiltrated heat through melting to ensure that the microenvironment temperature of the hollow optical fiber does not rise suddenly. The second stage, also known as the mid-stage fire, occurs at approximately 400°C to 800°C: If heat continues to penetrate, the self-expanding ceramic flame-retardant layer is activated, and the expanded graphite expands and compacts, forming a thicker heat insulation barrier. The third stage, also known as extreme fire, at temperatures above 800°C, involves the complete sintering of the self-expanding ceramic flame-retardant layer into a hard shell, providing a certain degree of resistance to mechanical impact. At this stage, the inner aerogel insulation buffer layer utilizes its extremely low thermal conductivity to prevent the final heat radiation and conduction from entering the hollow optical fiber.

[0085] The three components achieve a "heat sink gradient" through a gradual decrease in heat flow gradient: external 1000℃ → expansion ceramic layer reduces the temperature to about 300℃ → phase change layer absorbs heat and maintains about 80℃ → aerogel layer insulates and buffers → hollow optical fiber operating temperature ≤ 70℃, thereby achieving the required flame retardant effect. In summary, the high flame-retardant hollow fiber optic cable of the present invention redesigns its overall structure by fully addressing the aforementioned technical challenges of hollow fiber optic cables, and makes targeted improvements to the specific structure and processing methods of some key components. Correspondingly, it can rationally utilize the gradient synergistic mechanism of "reflective heat insulation + phase change heat absorption + expansion carbonization" to ensure that the hollow fiber optic cable maintains the safety threshold of telecommunications-grade equipment in high-temperature environments and achieves higher fire resistance integrity. Simultaneously, compared with existing technologies, it effectively solves the problem of heat convection sensitivity caused by the hollow interior of the fiber, ensuring the phase stability of the optical transmission path within the fiber core. Furthermore, it allows for more convenient and active control of the critical temperature inside the hollow fiber optic cable. Therefore, it is particularly suitable for high flame-retardant hollow fiber optic cable applications with extremely high fire safety requirements, such as data centers, rail transportation, ships, and high-rise buildings, and has broad application prospects.

[0086] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A high flame-retardant hollow optical fiber cable with gradient heat insulation and self-extinguishing fire mechanism, characterized in that, This high flame-retardant hollow fiber optic cable comprises, from the inside out, hollow fiber units, an aerogel thermal insulation buffer layer, a microcapsule phase change heat absorption layer, a self-expanding ceramicized flame-retardant layer, and a low-smoke halogen-free outer sheath layer, wherein: The hollow fiber unit includes a hollow fiber and an inner sleeve, wherein the hollow fiber is placed in the inner sleeve and filled with nitrogen. The aerogel thermal insulation buffer layer uses nanoporous silica aerogel as the substrate to block external heat from being conducted into the solid state of the hollow optical fiber unit. The microcapsule phase change heat absorption layer undergoes a phase change and absorbs heat after the external temperature reaches a preset value, which is used to actively absorb heat that seeps in from the outside. The self-expanding ceramic flame-retardant layer is premixed from multiple components, which, by weight, include: polyolefin base material, 40 to 60 parts; ceramic powder, 25 to 40 parts; and expandable graphite, 10 to 20 parts. In addition, during the preparation of the aerogel heat insulation buffer layer, the microcapsule phase change heat absorption layer, and the self-expanding ceramic flame retardant layer, nitrogen gas is continuously introduced into the inner sleeve and kept at positive pressure to ensure that the hollow optical fiber is always in an unpressurized state.

2. The high flame-retardant hollow optical fiber cable as described in claim 1, characterized in that, For the hollow fiber unit, it adopts anti-resonant or photonic bandgap hollow fiber with air core; in addition, the outer surface of the hollow fiber needs to be stripped of the original acrylate coating layer and then uniformly coated with polyimide coating or silicone resin coating.

3. The high flame-retardant hollow optical fiber cable as described in claim 2, characterized in that, For the hollow fiber unit, the hollow fiber is in a free and loose state with a gap of 0.1mm to 0.2mm in the inner sleeve; the outer side of the inner sleeve is preferably also wrapped with non-woven fabric or water-blocking yarn to absorb any moisture that may seep in and to provide additional buffering.

4. The high flame-retardant hollow optical fiber cable as described in any one of claims 1-3, characterized in that, The inner sleeve is prepared by an extrusion process, and during the extrusion process, positive pressure dry nitrogen gas of 0.01MPa to 0.03MPa is preferably introduced into the channel between the extruder head and the hollow optical fiber.

5. The high flame-retardant hollow optical fiber cable as described in any one of claims 1-4, characterized in that, For the aerogel thermal insulation buffer layer, nanoporous silica aerogel is preferably used as the substrate, and the relevant key parameters are set as follows: Aerogel pore size: 25nm~50nm; aerogel mass fraction: 15%~30%; thickness of aerogel thermal insulation buffer layer: 1.0mm~2.0mm; aerogel porosity retention rate: ≥85%; temperature gradient with adjacent interface: ≥200℃ / mm.

6. The high flame-retardant hollow optical fiber cable as described in any one of claims 1-5, characterized in that, The microcapsule phase change heat-absorbing layer comprises multiple microcapsules dispersed in a flexible matrix. Each microcapsule uses a phase change material such as paraffin and salt as its core and a thermosetting polymer such as melamine-formaldehyde resin as its shell. The flexible matrix is ​​preferably made of silicone rubber.

7. The high flame-retardant hollow optical fiber cable as described in any one of claims 1-6, characterized in that, For the self-expanding ceramic flame-retardant layer, its composition preferably further includes the following additives, by weight: Silane coupling agent, 1 to 2 parts; antioxidant, 0.5 to 1 part; lubricant, 1 to 2 parts.

8. The high flame-retardant hollow optical fiber cable as described in claim 7, characterized in that, The self-expanding ceramic flame-retardant layer is preferably prepared by the following process steps: Ingredients and dry mixing: Weigh each component according to the set ingredient ratio, premix the ceramic powder and the expandable graphite in a high-speed mixer for 3 to 5 minutes, then add the silane coupling agent and continue mixing for more than 5 minutes to obtain a dry mixture and modify the surface of the powder. Twin-screw compounding: The above dry mixture and the polyolefin base material are fed into a co-rotating twin-screw extruder for melt compounding. The relevant process parameters are as follows: screw length-to-diameter ratio: 44:1 to 52:1; screw speed: 250 rpm to 350 rpm. Vacuum exhaust: Turn on the vacuum pump in the exhaust section, with a vacuum degree ≤ –0.06MPa, to remove moisture and low molecular weight volatiles; Granulation and drying: The uniformly mixed material is granulated and dried at 80℃~100℃ for more than 4 hours to ensure that the moisture content is ≤0.1% and to avoid the generation of air bubbles during extrusion.

9. The high flame-retardant hollow optical fiber cable as described in any one of claims 1-8, characterized in that, The aerogel heat insulation buffer layer, microcapsule phase change heat absorption layer, and self-expanding ceramic flame retardant layer are preferably multi-layered and coated in one step through a co-extrusion process.

10. The high flame-retardant hollow optical fiber cable as described in any one of claims 1-9, characterized in that, For the low-smoke halogen-free outer sheath layer, it is preferably designed as a double layer, wherein the inner layer is made of polyolefin oxygen barrier material, and the outer layer is made of ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer as matrix resin, magnesium hydroxide as the main flame retardant, and also contains a variety of synergistic flame retardants, namely fibrous hydrous magnesium silicate, silicate natural minerals, and polyolefin NP flame retardant.

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