Flame-retardant optical cable with gradient structure

Abstract

This application belongs to the field of optical cables, specifically disclosing a flame-retardant optical cable with a gradient structure, comprising a cable core and an inner sheath, a middle sheath, and an outer sheath sequentially covering the outer side of the cable core from the inside out; the inner sheath is a porous buffer layer made of flame-retardant material; the middle sheath is a foamed flame-retardant layer; and the outer sheath is a high-density flame-retardant layer, with the density and flame-retardant rating of the inner, middle, and outer sheaths increasing sequentially. Through the structural design of this application, the three sheath structures of the inner, middle, and outer layers work synergistically to significantly reduce the overall weight of the optical cable while maintaining its excellent flame-retardant performance and mechanical strength, and improve its bending flexibility. This avoids the defects of existing metal-reinforced optical cables, such as high weight and poor bending performance, and non-metallic-reinforced optical cables, such as insufficient mechanical strength, achieving a unity of efficient flame retardancy, buffer protection, and lightweighting.

Description

Technical Field

[0001] This application belongs to the field of optical cables, and more specifically, relates to a flame-retardant optical cable with a gradient structure. Background Technology

[0002] Currently, flame-retardant optical cables are widely used in communication networks. Existing mainstream products use a loose-tube stranded structure as their core architecture and are mainly divided into two types based on whether the reinforcing components and armor materials contain metal: metal-reinforced and non-metal-reinforced. Each type has its own emphasis on flame retardancy, water resistance, and mechanical protection, forming the basic technical landscape of current flame-retardant optical cables.

[0003] In related technologies, metal-reinforced flame-retardant optical cables (such as GYTZA and GYTAH58) have an optical fiber structure placed inside a loose tube, twisted around a metal / non-metal reinforcing core, with the core fully filled with water-blocking material, covered with multiple layers of flame-retardant sheath, and often supplemented with steel or aluminum tape armor. This type of optical cable has reliable flame-retardant, water-blocking, and mechanical protection performance, but due to the stacking of multiple layers of flame-retardant material and armor layers, it has a large outer diameter and high weight. Furthermore, limited by the bending performance bottleneck of existing flame-retardant materials, its bending performance is generally poor, with a static bending radius typically not less than 12.5 times the cable diameter, insufficient flexibility, and difficult laying operations. Non-metallic reinforced flame-retardant optical cables (such as GYFTZY) use a non-metallic reinforcing core, a dry water-blocking method, no metal components, and introduce multiple aramid or glass fiber reinforcing yarns to improve mechanical performance, covered with a single layer of flame-retardant sheath. This type of optical cable is lightweight and has strong bending performance, but its mechanical strength (especially its resistance to lateral pressure, impact and tensile strength) is difficult to meet the requirements of harsh working conditions such as direct burial or high mechanical stress. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a flame-retardant optical cable with a gradient structure, aiming to solve the problem that existing flame-retardant optical cables cannot simultaneously meet the requirements of bending performance, mechanical strength, and lightweight design.

[0005] This application provides a flame-retardant optical cable with a gradient structure, specifically including a cable core and an inner sheath, a middle sheath, and an outer sheath that are sequentially wrapped around the outside of the cable core from the inside out; the inner sheath is a porous buffer layer made of flame-retardant material; the middle sheath is a foamed flame-retardant layer; and the outer sheath is a high-density flame-retardant layer, wherein the density and flame-retardant rating of the inner sheath, middle sheath, and outer sheath all increase sequentially.

[0006] Compared with the prior art, the optical cable adopts a three-layer gradient structure consisting of an inner porous buffer layer, a middle foamed flame-retardant layer, and an outer high-density flame-retardant layer. The density and flame-retardant rating of each sheath layer increase sequentially from the inside to the outside. This allows the inner porous structure to absorb and buffer energy and fix the cable core when the optical cable is subjected to external impact. The middle foamed layer further buffers and achieves weight reduction through the foam pores, while the outer high-density layer provides core flame-retardant protection and high mechanical strength. The three-layer structure works synergistically to significantly reduce the overall weight of the optical cable and improve bending flexibility while maintaining excellent flame-retardant performance. This avoids the defects of existing metal-reinforced optical cables, such as large weight and poor bending performance, and non-metal-reinforced optical cables, such as insufficient mechanical strength. It achieves a unity of efficient flame retardancy, buffer protection, and lightweighting.

[0007] As a further preferred embodiment, the porous buffer layer is a honeycomb structure made of flame-retardant PE material with a porosity of 65%-85%. The honeycomb structure includes multiple honeycomb units with a regular hexagonal structure and the wall thickness of the honeycomb unit is 0.1mm-0.5mm.

[0008] As a further preferred embodiment, the interior of the cellular unit is filled with nano-flame-retardant gel.

[0009] As a further preferred embodiment, the foamed flame-retardant layer is made by mixing Class A flame-retardant materials with a foaming agent and then performing a foaming process.

[0010] As a further preferred embodiment, the amount of foaming agent added is 5%-8% of the mass of the Class A flame retardant material, and the foaming ratio is 1.8-2.2 times.

[0011] As a further preferred option, the Class A flame retardant material is a low-smoke, halogen-free flame-retardant polyolefin.

[0012] As a further preferred embodiment, the outer sheath is made of a highly flame-retardant fluoroplastic material, wherein a nano-level flame-retardant modifier is added to the highly flame-retardant fluoroplastic material, and the oxygen index of the outer sheath is ≥40%.

[0013] As a further preferred embodiment, the high flame-retardant fluoroplastic material is at least one of PFA fluoroplastic, FEP fluoroplastic, or ETFE fluoroplastic.

[0014] As a further preferred embodiment, the nano-scale flame retardant modifier is a compound modifier of aluminum hydroxide and magnesium hydroxide, with a compound mass ratio of 1:0.5-1:2, and the amount of the nano-scale flame retardant modifier added is 12%-15%.

[0015] As a further preferred embodiment, the cable core includes a central reinforcing member and multiple cable units, the multiple cable units being twisted together on the central reinforcing member, each cable unit including a loose tube and several optical fiber units disposed within the loose tube, the space between the loose tube and the optical fiber units being filled with water-blocking fiber grease.

[0016] As a further preferred embodiment, the loose sleeve is made of flame-retardant PBT material.

[0017] As a further preferred embodiment, the inner sheath, the middle sheath, and the outer sheath are integrally formed by a three-layer co-extrusion process.

[0018] As a further preferred embodiment, the flame-retardant optical cable is an overall hexagonal tubular structure with rounded corners.

[0019] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages: 1. In this application, the outer layer of high-density flame-retardant material rapidly forms a dense char layer upon contact with fire, blocking the spread of flames and heat conduction. The middle foam layer further expands upon heating, thickening the heat insulation barrier and absorbing heat. The inner honeycomb structure, combined with nano-flame-retardant gel, provides secondary buffering and auxiliary heat insulation. Under flame erosion, the three-layer structure forms a synergistic flame-retardant system of "outer layer charring and oxygen isolation - middle layer expansion and heat insulation - inner layer heat absorption and buffering," exhibiting excellent flame-retardant performance while also taking into account buffering performance, thus solving the problem that existing optical cables cannot coordinate flame retardancy and buffering.

[0020] 2. This application significantly reduces the overall weight of the optical cable while ensuring mechanical strength by designing the middle sheath as a foamed layer and using a regular hexagonal honeycomb structure as the inner sheath. The middle foamed layer forms a uniform closed-cell foam structure through a foaming agent, reducing material usage; the inner honeycomb structure has high porosity, further reducing material consumption. Simultaneously, the outer high-density flame-retardant layer provides core mechanical protection, and the regular hexagonal irregular structure itself has higher lateral pressure resistance. This achieves a gradient distribution of "high-density load-bearing outer layer, low-density lightweight middle layer, and medium-density honeycomb fixation inner layer," significantly reducing the weight of the optical cable while maintaining excellent mechanical performance.

[0021] 3. This application employs a dual-layer buffering design, consisting of an inner honeycomb-structured porous buffer layer and a middle foamed flame-retardant layer, combined with nano-flame-retardant gas gel filled within the honeycomb units of the inner sheath, forming a gradient buffering system. The highly dense flame-retardant layer disperses the concentrated external load into a distributed load, the middle foamed flame-retardant layer absorbs impact energy through compression deformation, and the honeycomb-structured porous buffer layer further uniformly transmits and buffers residual stress, avoiding stress concentration caused by abrupt changes in the interlayer elastic modulus. Simultaneously, the middle foamed flame-retardant layer, acting as a flexible deformation layer, absorbs the main deformation during optical cable bending, reducing bending stress in the inner sheath and cable core, effectively improving the bending flexibility of the optical cable. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the cross-sectional structure of the flame-retardant optical cable provided in the embodiments of this application.

[0023] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1. Cable core; 11. Central reinforcement; 12. Cable unit; 121. Loose tube; 122. Fiber optic unit; 2. Inner sheath; 21. Cellular unit; 3. Middle sheath; 4. Outer sheath. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0025] Reference Figure 1 This application discloses a flame-retardant optical cable with a gradient structure, comprising a cable core 1, an inner sheath 2, a middle sheath 3, and an outer sheath 4. The inner sheath 2, the middle sheath 3, and the outer sheath 4 constitute a three-layer gradient flame-retardant structure, enabling the flame-retardant optical cable to maintain good flame-retardant performance while also meeting the requirements for bending performance, mechanical strength, and lightweight design.

[0026] In this embodiment, the inner sheath 2, the middle sheath 3, and the outer sheath 4 are integrally formed through a three-layer co-extrusion process, with seamless fusion between the layers. This effectively avoids the problem of easy delamination and peeling of traditional segmented sheaths, improving the overall integrity and structural stability of the flame-retardant optical cable. Simultaneously, the flame-retardant optical cable has an overall hexagonal tubular structure with rounded corners. Compared to the traditional circular structure, the hexagonal irregular structure makes the optical cable less prone to rolling and displacement, offering greater adaptability and meeting the needs of irregular laying scenarios such as equipment cabinets, irregular brackets, and narrow pipes. Furthermore, the hexagonal structure has higher mechanical strength and superior lateral pressure resistance, while the rounded corners enhance construction safety and reduce edge wear.

[0027] The inner sheath 2, middle sheath 3, and outer sheath 4 are sequentially wrapped around the outside of the cable core 1 from the inside out. The cable core 1 includes a central reinforcing member 11 and multiple cable units 12. In this embodiment, there are 6 cable units 12, which are twisted onto the central reinforcing member 11 using an SZ twisting method. The central reinforcing member is made of FRP material. Each cable unit 12 includes a loose tube 121 and several optical fiber units 122. In this embodiment, there are 7 optical fiber units 122, which are all located inside the loose tube 121. Water-blocking grease is filled between the loose tube 121 and the optical fiber units 122. The loose tube 121 is made of flame-retardant PBT material, which can achieve water-blocking sealing, improve the flame-retardant effect, and prevent moisture from entering and affecting the optical fiber transmission performance.

[0028] In this embodiment, the inner sheath 2 is a porous buffer layer made of flame-retardant material, which directly and tightly covers the outside of the cable core 1, serving to buffer and dampen shocks, fix the cable core 1, and provide auxiliary heat insulation. The middle sheath 3 is a foamed flame-retardant layer, which is tightly attached to the outside of the inner sheath 2, serving to provide transitional flame retardancy and lightweight buffering. The outer sheath 4 is a high-density flame-retardant layer, which is tightly attached to the outside of the middle sheath 3, serving to provide core flame retardancy, oxygen isolation, and heat insulation. The density and flame retardancy rating of the inner sheath 2, middle sheath 3, and outer sheath 4 all increase sequentially, forming a dual gradient distribution of density and flame retardant performance, laying the structural foundation for subsequent synergistic flame retardancy and gradient buffering.

[0029] Specifically, the porous buffer layer is a honeycomb structure made of flame-retardant PE material with a porosity of 65%-85%. The honeycomb structure comprises multiple hexagonal honeycomb units 21, each with a wall thickness of 0.1mm-0.5mm. This design achieves lightweighting while maintaining the stability of the honeycomb structure. The interior of each honeycomb unit 21 is filled with nano-flame-retardant gel. The honeycomb structure of the porous buffer layer provides cushioning, shock absorption, and cable core 1 fixation. The filling of the honeycomb units 21 with nano-flame-retardant gel further enhances the buffering performance and heat insulation / flame retardant effect. Simultaneously, the porous honeycomb structure achieves lightweighting of the optical cable, reducing material usage.

[0030] Furthermore, the foamed flame-retardant layer is made by mixing Class A flame-retardant material with a foaming agent and then performing a foaming process. In this embodiment, the Class A flame-retardant material is a low-smoke, halogen-free flame-retardant polyolefin, which is safe and environmentally friendly. It produces extremely low smoke and non-toxic, non-corrosive gases during combustion, effectively reducing secondary injuries in a fire. It also possesses good flame-retardant and processing properties, is easy to extrude and mold, causes minimal wear on equipment, and has a low density, helping to reduce product weight and overall costs. The amount of foaming agent added is 5%-8% of the mass of the Class A flame-retardant material, with a foaming ratio of 1.8-2.2 times. This ratio effectively maintains the Class A flame-retardant performance and material mechanical strength while significantly reducing weight and costs. After foaming, a uniform closed-cell foam structure is formed, which improves cushioning performance, reduces material usage, and lowers production costs. Simultaneously, the Class A flame-retardant material ensures that the flame-retardant rating of the middle layer meets the standards, achieving a gradient transition of flame-retardant performance from the middle layer to the outer layer.

[0031] Furthermore, the outer sheath 4 is made of a highly flame-retardant fluoroplastic material, which is at least one of PFA fluoroplastic, FEP fluoroplastic, or ETFE fluoroplastic. A nano-level flame-retardant modifier is added to the highly flame-retardant fluoroplastic material. This nano-level flame-retardant modifier is a compound modifier of aluminum hydroxide and magnesium hydroxide, with a compound mass ratio of 1:0.5-1:2. The addition amount of the nano-level flame-retardant modifier is 12%-15%, meaning the volume fraction of the nano-level flame-retardant modifier accounts for 12%-15% of the total material of the outer sheath 4. Too low an addition amount results in insufficient char formation and anti-dripping properties, while too high an addition amount affects processing fluidity and mechanical properties. The oxygen index of the outer sheath 4 is ≥40%. The outer sheath 4 does not drip or carbonize at high temperatures and can quickly form a dense char layer, blocking flame spread and heat conduction, thus playing a core flame-retardant protective role.

[0032] This application achieves a gradient transition in flame-retardant performance by setting up a three-layer gradient flame-retardant structure: an outer layer of high-density flame-retardant material, a middle layer of Class A foamed flame-retardant material, and an inner layer of honeycomb-structured porous buffer material. The high-flame-retardant fluoroplastic of the outer sheath plays a core role in oxygen and heat insulation; the middle sheath's Class A foamed flame-retardant layer provides transitional flame retardancy and lightweight buffering; and the inner sheath's honeycomb-structured porous buffer layer provides secondary buffering and auxiliary heat insulation. The three layers work synergistically to form a flame-retardant relay chain under flame erosion: "outer layer charring and oxygen isolation—middle layer expansion and heat insulation—inner layer heat absorption and buffering," resulting in excellent flame-retardant performance while also considering buffering performance, thus solving the problem of the inability of existing optical cables to coordinate flame retardancy and buffering.

[0033] Furthermore, due to the adoption of a three-layer gradient structure consisting of an inner porous buffer layer, a middle foamed flame-retardant layer, and an outer high-density flame-retardant layer, with the density and flame-retardant rating of each sheath layer increasing sequentially from the inside out, the inner porous structure can absorb and buffer energy and fix the cable core 1 when the optical cable is subjected to external impact. The middle foamed layer further buffers and achieves weight reduction through the foam pores, while the outer high-density layer provides core flame-retardant protection and high mechanical strength. The synergistic effect of the three-layer structure significantly reduces the overall weight of the optical cable and improves its bending flexibility while maintaining excellent flame-retardant performance. This avoids the shortcomings of existing metal-reinforced optical cables, such as high weight and poor bending performance, and non-metallic reinforced optical cables, which suffer from insufficient mechanical strength, thus achieving a balance between efficient flame retardancy, buffer protection, and lightweight design.

[0034] The following is an illustration through specific examples: Example 1: This embodiment provides a flame-retardant optical cable with a gradient structure. The flame-retardant optical cable has an overall hexagonal tubular structure with an outer circle diameter of 11 mm and rounded corners. The cable core 1 includes a central reinforcing member and six cable units 12. The central reinforcing member has a diameter of 2.5 mm. The six cable units 12 contain a total of 42 optical fiber units 122, which use flame-retardant PBT loose tubes 121. The loose tubes 121 have an outer diameter of 2.5 mm and a wall thickness of 0.35 mm. Water-blocking fiber optic paste is filled between the loose tubes 121 and the optical fiber units 122. The inner sheath 2 is a honeycomb structure made of flame-retardant PE material with a porosity of 75%. The honeycomb units 21 have a regular hexagonal structure with a honeycomb layer thickness of 0.3 mm, and the honeycomb units 21 are filled with nano-flame-retardant gel. The middle sheath 3 is a low-smoke, halogen-free, flame-retardant polyolefin foam layer. The foaming agent content is 6.5% of the mass of Class A flame-retardant material, with a foaming ratio of 2.0 times. After foaming, it forms a uniform closed-cell foam structure with a closed-cell rate of 88% and an average cell diameter of 80μm, with a thickness of 0.2mm. The outer sheath 4 is PFA fluoroplastic, with added aluminum hydroxide and magnesium hydroxide compound modifiers in a 1:1 mass ratio, added at a level of 13.5%. The oxygen index of the outer sheath 4 is 43%, and its thickness is 1.0mm. The inner sheath 2, middle sheath 3, and outer sheath 4 are integrally formed through a three-layer co-extrusion process.

[0035] Testing revealed that the optical cable in this embodiment exhibits a static bending radius of 8.5 times the cable diameter, a lateral pressure resistance of 2200 N / 100 mm, impact resistance with no fiber breakage after 15 impacts, a weight per unit length of 38 g / m, an oxygen index of 43%, and a flame retardancy rating of Class A. These results demonstrate that the optical cable in this embodiment demonstrates excellent performance in bending performance, mechanical strength, lightweighting, and flame retardancy. Its static bending radius is significantly superior to that of metal-reinforced optical cables (≥12.5 times the cable diameter), its lateral pressure resistance reaches or exceeds that of metal-reinforced optical cables (1800-2000 N / 100 mm), and its weight per unit length is reduced by approximately 30% compared to metal-reinforced optical cables. Simultaneously, it meets the B1 flame retardancy requirements, successfully balancing the triple requirements of bending performance, mechanical strength, and lightweighting.

[0036] Example 2: This embodiment provides a flame-retardant optical cable with a gradient structure. The cable is an overall hexagonal tubular structure with an outer diameter of 8mm and rounded corners. The cable core 1 includes six optical fiber units 122, using flame-retardant PBT loose tubes 121. The loose tubes 121 have an outer diameter of 2.0mm and a wall thickness of 0.3mm. Water-blocking fiber grease is filled between the loose tubes 121 and the optical fiber units 122. The outer diameter of the central reinforcing member is 1.4mm. The inner sheath 2 is a honeycomb structure made of flame-retardant PE material with a porosity of 80%. The honeycomb units 21 are hexagonal with a honeycomb layer thickness of 0.2mm, and are filled with nano-flame-retardant gel. The middle sheath 3 is a low-smoke, halogen-free, flame-retardant polyolefin foam layer. The foaming agent content is 7.5% of the mass of Class A flame-retardant material, with a foaming ratio of 2.1 times. After foaming, it forms a uniform closed-cell foam structure with a closed-cell rate of 85% and an average cell diameter of 100μm, with a thickness of 0.2mm. The outer sheath 4 is FEP fluoroplastic, with added aluminum hydroxide and magnesium hydroxide compound modifiers at a mass ratio of 1:0.8 and an addition amount of 14%. The oxygen index of the outer sheath 4 is 41%, and its thickness is 0.8mm. The inner sheath 2, middle sheath 3, and outer sheath 4 are integrally formed by a three-layer co-extrusion process.

[0037] Testing revealed that the optical cable of this embodiment has a static bending radius of 7.2 times the cable diameter, a lateral pressure resistance of 1950 N / 100 mm, and exhibits no fiber breakage after 12 impacts. Its weight per unit length is 32 g / m, its oxygen index is 41%, and its flame retardancy rating reaches Class A. Compared to Embodiment 1, this embodiment uses a more compact size (8 mm circumscribed circle diameter), further improving bending performance. With a static bending radius of only 7.2 times the cable diameter, it is suitable for laying scenarios with more limited space. Its weight per unit length is only 32 g / m, approximately 40% lower than that of metal-reinforced optical cables, resulting in a more significant weight reduction effect. The lateral pressure resistance of 1950 N / 100 mm still reaches the upper-middle level of metal-reinforced optical cables, meeting conventional mechanical protection requirements. This embodiment demonstrates that, with a more compact size, the technical solution of this application can still achieve a good balance between bending performance, mechanical strength, and lightweighting.

[0038] To further verify the superiority of the technical solution of this application, the following comparative test was conducted using control examples.

[0039] Compare with Example 1: The same cable core 1, inner sheath 2, and outer sheath 4 as in Example 1 were used, but the middle sheath 3 was omitted, and a two-layer co-extrusion molding process was employed. Testing showed that the static bending radius of the optical cable in Example 1 was 11.2 times the cable diameter, the lateral pressure resistance was 1650 N / 100 mm, the weight per unit length was 45 g / m, and the oxygen index was 42%. This demonstrates that removing the foamed flame-retardant middle layer significantly increased the bending radius and decreased the lateral pressure resistance of the optical cable. This indicates that the foamed flame-retardant middle layer, acting as a flexible deformation layer, absorbs the main deformation during bending to improve bending performance. Simultaneously, the closed-cell foam structure absorbs impact energy through pore compression deformation to enhance lateral pressure resistance, and its low-density characteristics effectively reduce the overall weight of the optical cable, making it a key layer for achieving a balance among these three aspects.

[0040] Compare with Example 2: The same three-layer sheath structure and parameters as in Example 1 were adopted, but the overall optical cable was a circular tubular structure (not a regular hexagon). Tests showed that the static bending radius of the optical cable in Example 2 was 9.1 times the cable diameter, the lateral pressure resistance was 1850 N / 100 mm, the weight per unit length was 39 g / m, and the oxygen index was 43%. This demonstrates that the lateral pressure resistance of the optical cable significantly decreased after adopting the circular structure. This indicates that the irregular hexagonal structure can evenly distribute the load along the sides of the hexagon to avoid stress concentration, thereby significantly improving lateral pressure resistance. Simultaneously, the flexible deformation of the foamed flame-retardant middle layer achieves a balance between rigid support and flexible bending.

[0041] Compare with Example 3: Using the same structure and parameters as Example 1, but without filling the honeycomb cells 21 of the inner sheath 2 with nano-flame-retardant gel. Tests showed that the static bending radius of the optical cable in Comparative Example 3 was 9.8 times the cable diameter, the lateral pressure resistance was 2100 N / 100 mm, the weight per unit length was 37 g / m, and the oxygen index was 39%. This demonstrates that omitting the nano-flame-retardant gel reduced the oxygen index of the optical cable to 39% and weakened its cushioning performance. This indicates that the nano-flame-retardant gel, with its extremely low thermal conductivity, effectively absorbs and blocks heat conduction during flame erosion, forming a triple flame-retardant barrier of "heat absorption—heat insulation—oxygen barrier" with the middle foamed flame-retardant layer and the outer high-density flame-retardant layer. Simultaneously, its nanoporous structure absorbs some strain energy through compression deformation during bending or impact, further improving bending and cushioning performance.

[0042] It should be understood that expressions such as "comprising" and "may include" as used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "comprising" and / or "having" may be interpreted as indicating a specific characteristic, number, operation, constituent element, component, or combination thereof, but should not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0043] It should be understood that the terms “center,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “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 application 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 application.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0045] In this application, unless otherwise expressly 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 connection; 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; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0046] 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 flame-retardant optical cable with a gradient structure, characterized in that, It includes a cable core (1) and an inner sheath (2), a middle sheath (3) and an outer sheath (4) that are sequentially wrapped around the outside of the cable core (1) from the inside out; the inner sheath (2) is a porous buffer layer made of flame retardant material, the middle sheath (3) is a foamed flame retardant layer, and the outer sheath (4) is a high-density flame retardant layer. The density and flame retardant rating of the inner sheath (2), the middle sheath (3) and the outer sheath (4) all increase sequentially.

2. The flame-retardant optical cable with a gradient structure as described in claim 1, characterized in that, The porous buffer layer is a honeycomb structure made of flame-retardant PE material with a porosity of 65%-85%. The honeycomb structure includes multiple honeycomb units (21) with a regular hexagonal structure and a wall thickness of 0.1mm-0.5mm for each honeycomb unit (21).

3. A flame-retardant optical cable with a gradient structure as described in claim 2, characterized in that, The interior of the cellular unit (21) is filled with nano-flame-retardant gel.

4. A flame-retardant optical cable with a gradient structure as described in claim 1, characterized in that, The foamed flame-retardant layer is made by mixing Class A flame-retardant materials with a foaming agent and then performing a foaming process.

5. A flame-retardant optical cable with a gradient structure as described in claim 4, characterized in that, The amount of foaming agent added is 5%-8% of the mass of the Class A flame retardant material, and the foaming ratio is 1.8-2.2 times.

6. A flame-retardant optical cable with a gradient structure as described in claim 4, characterized in that, The Class A flame retardant material is a low-smoke, halogen-free flame retardant polyolefin.

7. A flame-retardant optical cable with a gradient structure as described in claim 1, characterized in that, The outer sheath (4) is made of a high flame-retardant fluoroplastic material, which contains a nano-level flame-retardant modifier, and the oxygen index of the outer sheath (4) is ≥40%.

8. A flame-retardant optical cable with a gradient structure as described in claim 7, characterized in that, The high flame-retardant fluoroplastic material is at least one of PFA fluoroplastic, FEP fluoroplastic or ETFE fluoroplastic; and / or, the nano-level flame-retardant modifier is a compound modifier of aluminum hydroxide and magnesium hydroxide, with a compound mass ratio of 1:0.5-1:2, and the amount of nano-level flame-retardant modifier added is 12%-15%.

9. A flame-retardant optical cable with a gradient structure as described in claim 1, characterized in that, The cable core (1) includes a central reinforcing member (11) and multiple cable units (12), the multiple cable units (12) are twisted on the central reinforcing member (11), the cable unit (12) includes a loose tube (121) and a plurality of optical fiber units (122) disposed in the loose tube (121), the space between the loose tube (121) and the optical fiber units (122) is filled with water-blocking fiber grease; and / or, the loose tube (121) is made of flame-retardant PBT material.

10. A flame-retardant optical cable with a gradient structure as described in claim 1, characterized in that, The inner sheath (2), the middle sheath (3) and the outer sheath (4) are integrally formed by a three-layer co-extrusion process; and / or, the flame-retardant optical cable is a regular hexagonal tubular structure with rounded corners.

Images