Optical cable, flame-retardant sheath material for optical cable and preparation method of flame-retardant sheath material

Abstract

The invention relates to the technical field of optical fibers, in particular to an optical cable, a flame-retardant sheath material for the optical cable and a preparation method of the flame-retardant sheath material. The flame-retardant sheath material for the optical cable adopts a double-layer composite structure; comprising an outer functional protective layer and an inner enhanced flame-retardant layer, wherein the outer functional protective layer is composed of raw materials such as ethylene-octylene copolymer and linear low-density polyethylene, and the inner enhanced flame-retardant layer contains efficient flame-retardant components such as linear low-density polyethylene, ethylene-octylene copolymer and surface-modified nano magnesium hydroxide, and aramid chopped fibers are added for enhancing performance. The preparation method comprises the following steps: respectively preparing two layers of master batches, compounding through a double-layer co-extrusion technology, adding the aramid chopped fibers into the inner layer on line, and finally carrying out vacuum setting to obtain a finished product. The obtained optical cable sheath material has excellent flame retardance, mechanical property and environmental adaptability, and can effectively improve the safety and service life of an optical cable.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, specifically to an optical cable, a flame-retardant sheath material for optical cables, and a method for preparing the same. Background Technology

[0002] In optical communication networks, the flame-retardant properties of optical cable sheaths are crucial for safety in fire scenarios. However, traditional sheath materials with single-layer structures often struggle to achieve high flame retardancy while also maintaining other necessary comprehensive properties.

[0003] There is a direct conflict between flame retardancy and basic mechanical and processing properties. To meet stringent flame retardancy standards, a large amount of halogen-free flame retardants (such as magnesium hydroxide) must be added to the polyolefin matrix. While a high proportion of filler effectively improves flame retardancy, it also significantly increases the material's brittleness, reduces tensile strength, and deteriorates melt flowability, leading to a series of problems such as extrusion difficulties, rough sheath surfaces, and increased wear on processing equipment. Single-layer sheath systems have multiple limitations when dealing with complex application environments. For example, outdoor laying requires the sheath to have excellent weather resistance to resist ultraviolet radiation and environmental aging, but commonly used anti-aging additives may interact with the flame retardant system, affecting its effectiveness; for ease of construction and maintenance, the sheath surface needs to have anti-adhesion properties, but adding lubricants may weaken interlayer bonding or the material's inherent strength. In addition, if there are interface gaps between the sheath and the internal metal armor or cable core, moisture channels and mechanical weak points can easily form, and traditional methods of adjusting the process or adding adhesive layers further increase the complexity and cost of the process.

[0004] To address the aforementioned issues, existing technological solutions still have significant shortcomings: for example, while introducing nanomaterials may offer the potential for synergistic performance improvement, it faces challenges such as difficulty in dispersion, complex processes, high costs, and uncertain long-term weather resistance; or it may employ a multi-layer co-extrusion structure to attempt functional layering, but the inner layer designed to achieve high flame retardancy often suffers from excessive filler, resulting in high brittleness and poor adhesion to the cable core. Furthermore, the traditional process of pre-mixing and granulating reinforcing fibers can lead to fiber breakage due to high-temperature shearing, significantly reducing the reinforcing effect.

[0005] Therefore, how to systematically solve the problems of flame retardancy, mechanical strength, processing performance and weather resistance of traditional single-layer optical cable sheaths, so as to ensure that optical cables can operate stably for a long time in complex environments, has become a key technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0006] Based on the problems existing in the above-mentioned background technology, the present invention proposes a flame-retardant sheath material for optical cables. The flame-retardant sheath material is a double-layer composite sheath, which includes an outer functional protective layer and an inner reinforcing flame-retardant layer. The outer functional protective layer is composed of ethylene-octene copolymer, linear low-density polyethylene, silicone masterbatch, polyethylene wax, antioxidant, and ultraviolet absorber. The inner reinforcing flame-retardant layer is composed of linear low-density polyethylene, ethylene-octene copolymer, surface-modified nano magnesium hydroxide, aluminum diethylphosphinate, zinc borate, zinc stearate, and aramid chopped fibers.

[0007] Preferably, the outer functional protective layer comprises, by weight, 60-75 parts ethylene-octene copolymer, 20-25 parts linear low-density polyethylene, 2-3 parts silicone masterbatch, 1-2 parts polyethylene wax, 0.3-0.5 parts antioxidant, and 0.5-1.0 parts UV absorber. The ethylene-octene copolymer and linear low-density polyethylene are selected as the matrix. The ethylene-octene copolymer provides excellent flexibility and low-temperature impact resistance, while the linear low-density polyethylene provides the necessary rigidity and processing stability. The proportionate mixing of the two achieves a balance between flexibility and rigidity. The silicone masterbatch and polyethylene wax constitute a composite lubrication system. The former mainly provides durable internal and external lubrication and a smooth surface feel to achieve anti-adhesion, while the latter focuses on improving melt flowability.

[0008] Preferably, the outer functional protective layer comprises, by weight, 60-75 parts ethylene-octene copolymer, 20-25 parts linear low-density polyethylene, 2-3 parts silicone masterbatch, 1-2 parts polyethylene wax, 0.3-0.5 parts antioxidant 1010, and 0.5-1.0 parts ultraviolet absorber UV-531. The combination of antioxidant 1010 and UV-531 constitutes a highly efficient protection system against heat oxidation and ultraviolet aging.

[0009] Preferably, the inner reinforcing flame retardant layer is composed of the following components by weight: 70 parts of linear low-density polyethylene, 30 parts of ethylene-octene copolymer, 25-35 parts of surface-modified nano magnesium hydroxide, 15-25 parts of aluminum diethylphosphines, 3-5 parts of zinc borate, 0.5-1 parts of zinc stearate; and 8-12% of aramid chopped fibers based on the total weight of the inner reinforcing flame retardant layer materials.

[0010] Preferably, the method for surface-modified nano-magnesium hydroxide is as follows: nano-magnesium hydroxide and silane coupling agent KH-550 are added to a high-speed mixer at a mass ratio of 10:1, and the mixture is stirred at 1000 rpm for 15 minutes at 120°C. The silanol groups generated by the hydrolysis of KH-550 undergo a condensation reaction with the hydroxyl groups on the surface of magnesium hydroxide, forming an organic monomolecular film on the particle surface. This significantly reduces the surface energy of the nano-magnesium hydroxide particles and effectively prevents their agglomeration during subsequent processing and storage.

[0011] Preferably, a method for preparing a flame-retardant sheath material for optical cables includes the following steps:

[0012] (1) The raw materials used to form the outer functional protective layer are mixed, melt extruded and granulated to obtain the outer functional protective layer masterbatch, forming a homogeneous material with anti-adhesion and weather resistance functions;

[0013] (2) Except for aramid short-cut fibers, the remaining raw materials used to form the inner layer of flame retardant reinforcement are mixed, melt-extruded and granulated to obtain the inner layer of flame retardant reinforcement masterbatch, forming a homogeneous base material with high flame retardant potential. At this time, the masterbatch does not contain aramid short-cut fibers.

[0014] (3) The outer functional protective layer masterbatch and the inner reinforcing flame retardant layer masterbatch prepared in steps (1) and (2) are respectively added to two extruders and compounded through a double-layer co-extrusion die. At the same time, aramid chopped fibers are added online to the extruded inner layer melt, so that the two layers of melt are compounded and wrapped around the cable core. Finally, vacuum shaping is performed to obtain the finished product. At this time, the addition of aramid chopped fibers can effectively avoid excessive wear and cutting at the front end of the solid conveying section and the high shear melting section. The high viscosity melt wraps around the aramid chopped fibers, and with the help of the gentle shearing of the screw, they are evenly dispersed but not severely damaged, maximizing the retention of their length and reinforcement effect.

[0015] Preferably, in step (1), the raw materials of the outer functional protective layer are mixed at 60-70°C and 800 rpm for 10-15 minutes before extrusion. Appropriate heating is beneficial for softening lubricants such as polyethylene wax and initially uniformly coating the surface of resin particles. On the other hand, this temperature is lower than the decomposition initiation temperature of antioxidants and ultraviolet absorbers, which can effectively prevent functional additives from failing in the pretreatment stage.

[0016] In step (1), the melt extrusion is performed using a twin-screw extruder at a temperature of 135-150℃, which is the plasticizing temperature. This temperature is designed to melt the outer layer masterbatch under relatively low and mild conditions to maximize the protection of organic additives such as antioxidants and UV absorbers from decomposition. The screw speed is 200 rpm to provide appropriate shear force and ensure uniform dispersion of components such as silicone. After the melt is extruded through the die, it immediately enters a cooling water bath with the water temperature controlled at 25-30℃ for rapid cooling and shaping to prevent excessive crystallization from affecting transparency and surface smoothness. The cooled strip is then cut into uniformly sized pellets by a pelletizer. Finally, the pellets are placed in an 85℃ circulating hot air oven for 4 hours to thoroughly remove any moisture that may have been adsorbed during processing, resulting in the outer functional protective layer masterbatch.

[0017] Preferably, in step (2), the raw materials of the inner layer reinforced flame retardant layer are mixed at 800 rpm at 20-25°C for 5-10 minutes before extrusion. The melt extrusion is performed using a twin-screw extruder, and the melt extrusion temperature is 155-170°C. The purpose of this higher temperature is to ensure that the inner layer base material filled with a large amount of inorganic flame retardant (such as surface-modified nano magnesium hydroxide) can be fully plasticized to obtain good melt flowability and dispersibility. The screw speed is 180 rpm, and the granulation method and parameters are consistent with the process of the outer layer functional protective layer masterbatch, and finally the inner layer reinforced flame retardant layer masterbatch is obtained.

[0018] Preferably, in step (3), the outer layer melt extrusion temperature of the two extruders is 135-150℃, the inner layer melt extrusion temperature is 155-170℃, and the temperature of the double-layer co-extrusion die is 160℃. In the double-layer co-extrusion, when the melt flows from the extruder outlet at 135-150℃ to the die at 160℃, it will be further heated, the viscosity will decrease, and the fluidity will improve. When the melt flows from the extruder outlet at 155-170℃ to the die at 160℃, it may be slightly cooled or held, and the viscosity will increase. By uniformly controlling the temperature of the die, the actual temperature and viscosity of the two layers of melt when they meet are made to be close to the same, thereby ensuring that they can flow parallel and stably together through the die flow channel to form a composite sheath with a clear interface and a strong bond. If the viscosity difference between the two layers of melt is too large, the interface will be unstable, the layer thickness will be uneven, or even the layers will penetrate each other (interlayer material flow), which will seriously affect the quality and performance of the sheath.

[0019] In step (3), the length of the aramid chopped fiber is 3-6 mm, and it is injected into the inner layer extruder at the end of the melting section and before the metering section through a lateral weightless feeder. At this time, the inner layer base material has been completely melted. The high viscosity melt can generate sufficient wrapping and shearing force on the fiber, so that it can be dispersed quickly. At the same time, it avoids the fiber from experiencing long-term high temperature and strong shear in the solid conveying section and the front end of the melting section of the screw, thereby protecting the length and strength of the fiber and maximizing its reinforcing effect. It is evenly dispersed in the inner layer melt in a complete form, so as to truly play the role of "skeleton" reinforcement and significantly improve the mechanical properties of the inner layer.

[0020] The vacuum degree of the vacuum forming is -0.07 MPa to -0.09 MPa, preferably -0.08 MPa. Under negative pressure, the melt is tightly adsorbed onto the surface of the cable core, and even some uneven areas on the surface can be tightly bonded, completely eliminating the air between the sheath and the cable core, ensuring tight bonding and long-term reliable protection.

[0021] Preferably, the optical cable is made from a flame-retardant sheath material for optical cables.

[0022] Compared to existing technologies, this invention solves the challenge of balancing flame retardancy, mechanical strength, and processing performance in traditional single-layer sheaths through innovative improvements in the double-layer composite sheath structure and material formulation. The inner layer uses surface-modified nano-magnesium hydroxide, uniformly dispersed through silane coupling agent treatment, forming a dense layer to block heat and oxygen transfer, significantly improving the flame retardancy rating. The outer layer uses a blend of ethylene-octene copolymer and linear low-density polyethylene as the matrix, balancing flexibility and rigidity. Combined with an antioxidant 1010 and UV absorber UV-531 compound system, it effectively resists ultraviolet radiation and damp heat aging. The online addition technology of aramid short-cut fibers avoids fiber breakage in traditional premixing processes, ensuring improved tensile strength of the inner layer. Simultaneously, the temperature control design of the double-layer co-extrusion die achieves melt viscosity matching, forming a robust composite structure. This invention optimizes weather resistance and flame retardancy through functional layering, and ensures the stability of organic additives through optimized processing technology, enabling long-term stable operation of the optical cable sheath in complex environments, greatly improving safety and service life. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] Raw material preparation for flame retardant sheath material

[0026] Raw materials for the outer functional protective layer: 70 parts by weight of ethylene-octene copolymer, 22 parts by weight of linear low-density polyethylene, 2 parts by weight of silicone masterbatch, 1 part by weight of polyethylene wax, 0.4 parts by weight of antioxidant, and 0.7 parts by weight of ultraviolet absorber.

[0027] Inner layer reinforced flame retardant material: 70 parts by weight of linear low-density polyethylene, 30 parts by weight of ethylene-octene copolymer, 30 parts by weight of surface-modified nano magnesium hydroxide, 20 parts by weight of aluminum diethylphosphines, 4 parts by weight of zinc borate, 0.7 parts by weight of zinc stearate; and aramid chopped fibers accounting for 10% of the total weight of the inner layer reinforced flame retardant material.

[0028] Preparation of flame-retardant sheath materials for optical cables

[0029] (1) Preparation of outer functional protective layer masterbatch: The weighed raw materials of the outer functional protective layer were put into a high-speed mixer and mixed at 800 rpm at 65°C for 12 minutes to soften the lubricant and make it evenly adhere to the surface of the resin particles. Then, the mixture was fed into a twin-screw extruder and melt extruded according to the temperature settings of 135°C in zone 1, 140°C in zone 2, 145°C in zone 3, 150°C in zone 4 and 150°C at the die head. The screw speed was 200 rpm. After the melt was cooled in a water bath and pelletized, it was dried at 85°C for 4 hours to obtain the outer functional protective layer masterbatch.

[0030] (2) Preparation of masterbatch for inner layer reinforcement flame retardant layer: First, the surface of nano-magnesium hydroxide was modified. The weighed nano-magnesium hydroxide and silane coupling agent KH-550 were added to a high-speed mixer at a mass ratio of 10:1. The mixture was stirred at 1000 rpm for 15 minutes at 120°C to form an organic coating layer on its surface. The modified nano-magnesium hydroxide and the remaining raw materials of the inner layer, except for the aramid short-cut fibers, were added to the mixer and mixed at 800 rpm for 7 minutes at 22°C. Then, the mixture was melt-granulated by a twin-screw extruder. The extrusion temperature was set as follows: Zone 1 155°C, Zone 2 160°C, Zone 3 165°C, Zone 4 170°C, and Die Head 165°C. The screw speed was 180 rpm. After the melt was cooled in a water bath and granulated, it was dried at 85°C for 4 hours to obtain the masterbatch for inner layer reinforcement flame retardant layer.

[0031] (3) Add the outer functional protective layer masterbatch and the inner reinforcing flame retardant layer masterbatch to two extruders respectively. Set the temperature of each section of the outer extruder to 135-150℃ and the temperature of each section of the inner extruder to 155-170℃. After the inner layer melt is plasticized, inject the aramid chopped fibers into the end of the melting section of the inner extruder through a side weightless feeder. Finally, extrude the inner and outer layer melts through a double-layer co-extrusion die. Set the temperature of the double-layer co-extrusion die to 160℃. Adjust the speed of the two extruders to match the flow rate of the inner and outer layer melts. The composite melt is wrapped around the cable core through the double-layer co-extrusion die. After wrapping, it immediately enters the vacuum shaping sleeve. Control the vacuum degree at -0.08 MPa to ensure that the sheath material is tightly attached to the cable core.

[0032] Example 2

[0033] Raw material preparation for flame retardant sheath material

[0034] Outer functional protective layer raw materials: 60 parts by weight of ethylene-octene copolymer, 20 parts by weight of linear low-density polyethylene, 2 parts by weight of silicone masterbatch, 1 part by weight of polyethylene wax, 0.3 parts by weight of antioxidant, and 0.5 parts by weight of ultraviolet absorber.

[0035] The raw materials for the inner layer reinforcement flame retardant layer are as follows: 70 parts by weight of linear low-density polyethylene, 30 parts by weight of ethylene-octene copolymer, 25 parts by weight of surface-modified nano magnesium hydroxide, 15 parts by weight of aluminum diethylphosphines, 3 parts by weight of zinc borate, 0.5 parts by weight of zinc stearate, and 8% by weight of aramid chopped fibers based on the total weight of the inner layer reinforcement flame retardant layer materials.

[0036] Preparation of flame-retardant sheath materials for optical cables

[0037] (1) Preparation of outer functional protective layer masterbatch: The weighed raw materials of the outer functional protective layer were put into a high-speed mixer and mixed at 800 rpm at 60°C for 10 minutes to soften the lubricant and make it evenly adhere to the surface of the resin particles. Then, the mixture was fed into a twin-screw extruder and melt extruded according to the temperature settings of 135°C in zone 1, 140°C in zone 2, 145°C in zone 3, 150°C in zone 4 and 150°C at the die head. The screw speed was 200 rpm. After the melt was cooled in a water bath and pelletized, it was dried at 85°C for 4 hours to obtain the outer functional protective layer masterbatch.

[0038] (2) Preparation of the inner layer reinforced flame retardant masterbatch: First, the surface of nano-magnesium hydroxide was modified. The weighed nano-magnesium hydroxide and silane coupling agent KH-550 were added to a high-speed mixer at a mass ratio of 10:1. The mixture was stirred at 1000 rpm for 15 minutes at 120°C to form an organic coating layer on its surface. The modified nano-magnesium hydroxide and the remaining raw materials of the inner layer, except for the aramid short-cut fibers, were added to the mixer and mixed at 800 rpm for 5 minutes at 20°C. The mixture was then melt-granulated through a twin-screw extruder. The extrusion temperature was set as follows: Zone 1: 155°C, Zone 2: 160°C, Zone 3: 165°C, Zone 4: 170°C, and Die Head: 165°C. The screw speed was 180 rpm. After the melt was cooled in a water bath and granulated, it was dried at 85°C for 4 hours to obtain the inner layer reinforced flame retardant masterbatch.

[0039] (3) Add the outer functional protective layer masterbatch and the inner reinforcing flame retardant layer masterbatch to two extruders respectively. Set the temperature of each section of the outer extruder to 135-150℃ and the temperature of each section of the inner extruder to 155-170℃. After the inner layer melt is plasticized, inject the aramid short-cut fiber into the end of the melting section of the inner layer extruder through a side weightless feeder. Finally, extrude the inner and outer layer melts through a double-layer co-extrusion die. Set the temperature of the double-layer co-extrusion die to 160℃. Adjust the speed of the two extruders to match the flow rate of the inner and outer layer melts. The composite melt is wrapped around the cable core through the double-layer co-extrusion die. After wrapping, it immediately enters the vacuum shaping sleeve. Control the vacuum degree at -0.07 MPa to make the sheath material tightly adhere to the cable core.

[0040] Example 3

[0041] Raw material preparation for flame retardant sheath material

[0042] Outer functional protective layer raw materials: 75 parts by weight of ethylene-octene copolymer, 25 parts by weight of linear low-density polyethylene, 3 parts by weight of silicone masterbatch, 2 parts by weight of polyethylene wax, 0.5 parts by weight of antioxidant, and 1.0 part by weight of ultraviolet absorber.

[0043] Inner layer reinforced flame retardant material: 70 parts by weight of linear low-density polyethylene, 30 parts by weight of ethylene-octene copolymer, 35 parts by weight of surface-modified nano magnesium hydroxide, 25 parts by weight of aluminum diethylphosphines, 5 parts by weight of zinc borate, 1 part by weight of zinc stearate, and aramid chopped fibers accounting for 12% of the total weight of the inner layer reinforced flame retardant material.

[0044] Preparation of flame-retardant sheath materials for optical cables

[0045] (1) Preparation of outer functional protective layer masterbatch: The weighed raw materials for the outer functional protective layer were put into a high-speed mixer and mixed at 70°C and 800 rpm for 15 minutes to soften the lubricant and make it evenly adhere to the surface of the resin particles. Then, the mixture was fed into a twin-screw extruder and melt extruded according to the temperature settings of 135°C in zone 1, 140°C in zone 2, 145°C in zone 3, 150°C in zone 4 and 150°C at the die head. The screw speed was 200 rpm. After the melt was cooled in a water bath and pelletized, it was dried at 85°C for 4 hours to obtain the outer functional protective layer masterbatch.

[0046] (2) Preparation of the inner layer reinforced flame retardant masterbatch: First, the surface of nano-magnesium hydroxide was modified. The weighed nano-magnesium hydroxide and silane coupling agent KH-550 were added to a high-speed mixer at a mass ratio of 10:1. The mixture was stirred at 1000 rpm for 15 minutes at 120°C to form an organic coating layer on its surface. The modified nano-magnesium hydroxide and the remaining raw materials of the inner layer, except for the aramid short-cut fibers, were added to the mixer and mixed at 800 rpm for 10 minutes at 25°C. The mixture was then melt-granulated through a twin-screw extruder. The extrusion temperature was set as follows: Zone 1: 155°C, Zone 2: 160°C, Zone 3: 165°C, Zone 4: 170°C, and Die Head: 165°C. The screw speed was 180 rpm. After the melt was cooled in a water bath and granulated, it was dried at 85°C for 4 hours to obtain the inner layer reinforced flame retardant masterbatch.

[0047] (3) The outer functional protective layer masterbatch and the inner reinforcing flame retardant layer masterbatch are added to two extruders respectively. The temperature of each section of the outer extruder is set to 135-150℃ and the temperature of each section of the inner extruder is set to 155-170℃. After the inner layer melt is plasticized, the aramid short-cut fiber is precisely injected into the end of the melting section of the inner layer extruder through a side weightless feeder. Finally, the inner and outer layer melts are composite extruded through a double-layer co-extrusion die. The temperature of the double-layer co-extrusion die is uniformly set to 160℃. The speed of the two extruders is adjusted to match the flow rate of the inner and outer layer melts. The composite melt is wrapped around the cable core through the double-layer co-extrusion die. After wrapping, it immediately enters the vacuum shaping sleeve. The vacuum degree is controlled at -0.09 MPa so that the sheath material is tightly attached to the cable core.

[0048] Example 4

[0049] Raw material preparation for flame retardant sheath material

[0050] Outer functional protective layer raw materials: 65 parts by weight of ethylene-octene copolymer, 23 parts by weight of linear low-density polyethylene, 2.5 parts by weight of silicone masterbatch, 1.5 parts by weight of polyethylene wax, 0.4 parts by weight of antioxidant 1010, and 0.6 parts by weight of ultraviolet absorber UV-531.

[0051] The raw materials for the inner layer reinforcement flame retardant layer are as follows: 70 parts by weight of linear low-density polyethylene, 30 parts by weight of ethylene-octene copolymer, 27 parts by weight of surface-modified nano magnesium hydroxide, 21 parts by weight of aluminum diethylphosphines, 3.5 parts by weight of zinc borate, 0.6 parts by weight of zinc stearate, and 9% by weight of aramid chopped fibers based on the total weight of the inner layer reinforcement flame retardant layer materials.

[0052] Preparation of flame-retardant sheath materials for optical cables

[0053] (1) Preparation of outer functional protective layer masterbatch: The weighed raw materials for the outer functional protective layer were put into a high-speed mixer and mixed at 800 rpm at 63°C for 13 minutes to soften the lubricant and make it evenly adhere to the surface of the resin particles. Then, the mixture was fed into a twin-screw extruder and melt extruded according to the temperature settings of 135°C in zone 1, 140°C in zone 2, 145°C in zone 3, 150°C in zone 4 and 150°C at the die head. The screw speed was 200 rpm. After the melt was cooled in a water bath and pelletized, it was dried at 85°C for 4 hours to obtain the outer functional protective layer masterbatch.

[0054] (2) Preparation of the inner layer reinforced flame retardant masterbatch: First, the surface of nano-magnesium hydroxide was modified. The weighed nano-magnesium hydroxide and silane coupling agent KH-550 were added to a high-speed mixer at a mass ratio of 10:1. The mixture was stirred at 1000 rpm for 15 minutes at 120°C to form an organic coating layer on its surface. The modified nano-magnesium hydroxide and the remaining raw materials of the inner layer, except for the aramid short-cut fibers, were added to the mixer and mixed at 800 rpm for 9 minutes at 23°C. The mixture was then melt-granulated through a twin-screw extruder. The extrusion temperature was set as follows: Zone 1: 155°C, Zone 2: 160°C, Zone 3: 165°C, Zone 4: 170°C, and Die Head: 165°C. The screw speed was 180 rpm. After the melt was cooled in a water bath and granulated, it was dried at 85°C for 4 hours to obtain the inner layer reinforced flame retardant masterbatch.

[0055] (3) Add the outer functional protective layer masterbatch and the inner reinforcing flame retardant layer masterbatch to two extruders respectively. Set the temperature of each section of the outer extruder to 135-150℃ and the temperature of each section of the inner extruder to 155-170℃. After the inner layer melt is plasticized, inject the aramid chopped fibers into the end of the melting section of the inner layer extruder through a side weightless feeder. Finally, extrude the inner and outer layer melts through a double-layer co-extrusion die. Set the temperature of the double-layer co-extrusion die to 160℃. Adjust the speed of the two extruders to match the flow rate of the inner and outer layer melts. The composite melt is wrapped around the cable core through the double-layer co-extrusion die. After wrapping, it immediately enters the vacuum shaping sleeve. Control the vacuum degree at -0.08MPa to ensure that the sheath material is tightly attached to the cable core.

[0056] Example 5

[0057] Raw material preparation for flame retardant sheath material

[0058] Outer functional protective layer raw materials: 72 parts by weight of ethylene-octene copolymer, 21 parts by weight of linear low-density polyethylene, 2 parts by weight of silicone masterbatch, 1 part by weight of polyethylene wax, 0.3 parts by weight of antioxidant 1010, and 0.8 parts by weight of ultraviolet absorber UV-531.

[0059] The raw materials for the inner layer reinforcement flame retardant layer are as follows: 70 parts by weight of linear low-density polyethylene, 30 parts by weight of ethylene-octene copolymer, 33 parts by weight of surface-modified nano magnesium hydroxide, 22 parts by weight of aluminum diethylphosphines, 4.5 parts by weight of zinc borate, 0.8 parts by weight of zinc stearate, and 11% by weight of aramid chopped fibers based on the total weight of the inner layer reinforcement flame retardant layer materials.

[0060] Preparation of flame-retardant sheath materials for optical cables

[0061] (1) Preparation of outer functional protective layer masterbatch: The weighed raw materials for the outer functional protective layer were put into a high-speed mixer and mixed at 800 rpm at 68°C for 11 minutes to soften the lubricant and make it evenly adhere to the surface of the resin particles. Then, the mixture was fed into a twin-screw extruder and melt extruded according to the temperature settings of 135°C in zone 1, 140°C in zone 2, 145°C in zone 3, 150°C in zone 4 and 150°C at the die head. The screw speed was 200 rpm. After the melt was cooled in a water bath and pelletized, it was dried at 85°C for 4 hours to obtain the outer functional protective layer masterbatch.

[0062] (2) Preparation of the inner layer reinforced flame retardant masterbatch: First, the surface of nano-magnesium hydroxide was modified. The weighed nano-magnesium hydroxide and silane coupling agent KH-550 were added to a high-speed mixer at a mass ratio of 10:1. The mixture was stirred at 1000 rpm for 15 minutes at 120°C to form an organic coating layer on its surface. The modified nano-magnesium hydroxide and the remaining raw materials of the inner layer, except for the aramid short-cut fibers, were added to the mixer and mixed at 800 rpm for 6 minutes at 21°C. The mixture was then melt-granulated through a twin-screw extruder. The extrusion temperature was set as follows: Zone 1: 155°C, Zone 2: 160°C, Zone 3: 165°C, Zone 4: 170°C, and Die Head: 165°C. The screw speed was 180 rpm. After the melt was cooled in a water bath and granulated, it was dried at 85°C for 4 hours to obtain the inner layer reinforced flame retardant masterbatch.

[0063] (3) Add the outer functional protective layer masterbatch and the inner reinforcing flame retardant layer masterbatch to two extruders respectively. Set the temperature of each section of the outer extruder to 135-150℃ and the temperature of each section of the inner extruder to 155-170℃. After the inner layer melt is plasticized, inject the aramid chopped fibers into the end of the melting section of the inner layer extruder through a side weightless feeder. Finally, extrude the inner and outer layer melts through a double-layer co-extrusion die. Set the temperature of the double-layer co-extrusion die to 160℃. Adjust the speed of the two extruders to match the flow rate of the inner and outer layer melts. The composite melt is wrapped around the cable core through the double-layer co-extrusion die. After wrapping, it immediately enters the vacuum shaping sleeve. Control the vacuum degree at -0.08MPa to ensure that the sheath material is tightly attached to the cable core.

[0064] Comparative Example 1

[0065] Comparative Example 1 uses a traditional single-layer sheath design. Its raw material is only a blend of linear low-density polyethylene and ethylene-octene copolymer, and it is filled with the same amount of surface-modified nano-magnesium hydroxide and aluminum diethylphosphinate flame retardants as the inner layer of Example 1. No aramid chopped fiber reinforcement is used. The remaining preparation steps and parameters are completely consistent with those in Example 1.

[0066] Comparative Example 2

[0067] Comparative Example 2 uses the same double-layer structure and basic formulation as Example 1, but changes the way aramid chopped fibers are added. These fibers are fed into a high-speed mixer along with other inner layer raw materials, and then melt-granulated at high temperature using a twin-screw extruder to obtain fiber-containing inner layer masterbatch. In subsequent co-extrusion steps, aramid chopped fibers are no longer added online. All other steps and parameters are completely consistent with Example 1.

[0068] Performance tests were conducted on Examples 1-5 and Comparative Examples 1-2, and the results are shown in the table below:

[0069] Table 1 Performance test results of flame-retardant sheath materials for optical cables

[0070] Group Tensile strength (MPa) Elongation at break (%) Limiting oxygen index (%) Example 1 23 353 33.8 Example 2 21 336 33.2 Example 3 20 337 33.5 Example 4 23 341 34.1 Example 5 22 346 34.3 Comparative Example 1 12 179 30.8 Comparative Example 2 15 217 31.2

[0071] As can be seen from the data in Table 1, the tensile strength of Examples 1-5 is significantly higher than that of the two comparative examples, and the limiting oxygen index of Examples 1-5 is higher than 33%, meeting the high flame retardancy standard. This indicates that the design can maintain its core flame retardant performance while achieving high strength. Although the performance of Comparative Example 2 is better than that of the single-layer structure, it is still significantly lower than that of the other examples. In summary, this invention successfully achieves a synergistic improvement in high flame retardancy and high mechanical properties through systematic innovation in materials and processes.

[0072] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A flame-retardant jacketing material for optical cables, characterized by: The flame-retardant sheath material is a double-layer composite sheath, which comprises an outer functional protective layer and an inner enhanced flame-retardant layer; the outer functional protective layer is composed of ethylene-octene copolymer, linear low-density polyethylene, silicone master batch, polyethylene wax, antioxidant and ultraviolet absorber; the inner enhanced flame-retardant layer is composed of linear low-density polyethylene, ethylene-octene copolymer, surface-modified nano magnesium hydroxide, aluminum diethyl phosphinate, zinc borate, zinc stearate and aramid short fibers.

2. A flame-retardant jacketing material for optical fiber cables according to claim 1, characterized in that: The outer functional protective layer is composed of ethylene-octene copolymer 60-75 parts, linear low-density polyethylene 20-25 parts, silicone master batch 2-3 parts, polyethylene wax 1-2 parts, antioxidant 0.3-0.5 parts and ultraviolet absorber 0.5-1.0 parts by weight.

3. A flame-retardant jacketing material for optical fiber cables according to claim 2, characterized in that: The outer functional protective layer is composed of ethylene-octene copolymer 60-75 parts, linear low-density polyethylene 20-25 parts, silicone master batch 2-3 parts, polyethylene wax 1-2 parts, antioxidant 1010 0.3-0.5 parts and ultraviolet absorber UV-531 0.5-1.0 parts by weight.

4. A flame-retardant jacketing material for optical fiber cables according to claim 1, characterized in that: The inner enhanced flame-retardant layer is composed of linear low-density polyethylene 70 parts, ethylene-octene copolymer 30 parts, surface-modified nano magnesium hydroxide 25-35 parts, aluminum diethyl phosphinate 15-25 parts, zinc borate 3-5 parts, zinc stearate 0.5-1 part and aramid short fibers accounting for 8-12% of the total weight of the inner enhanced flame-retardant layer material.

5. A flame-retardant jacket material for optical fiber cables according to claim 4, characterized in that: The method for surface modification of nano magnesium hydroxide is as follows: nano magnesium hydroxide and silane coupling agent KH-550 are put into a high-speed mixer at a mass ratio of 10:1, and stirred at a high speed of 1000 rpm at a temperature of 120℃ for 15 minutes.

6. A method for preparing a flame-retardant sheath material for optical cables according to any one of claims 1-5, characterized in that: The method comprises the following steps, (1) the raw materials for forming the outer functional protective layer are mixed, melt-extruded and granulated to obtain outer functional protective layer master batch; (2) the raw materials for forming the inner enhanced flame-retardant layer are mixed, melt-extruded and granulated except for aramid short fibers to obtain inner enhanced flame-retardant layer master batch; (3) the outer functional protective layer master batch and the inner enhanced flame-retardant layer master batch prepared in steps (1) and (2) are respectively added into two extruders, and are extruded through a double-layer co-extrusion die, while aramid short fibers are added into the extruded inner melt on line, so that the two layers of melt are compounded and coated on the cable core, and finally vacuum setting is performed to obtain the finished product.

7. The method for preparing a flame-retardant sheath material for optical cables according to claim 6, characterized in that: In step (1), the raw materials of the outer functional protective layer are mixed at 60-70℃ and 800 rpm for 10-15 minutes before extrusion, the melt-extrusion is performed by using a double-screw extruder, and the melt-extrusion temperature is 135-150℃ and the screw rotation speed is 200 rpm.

8. The method for preparing a flame-retardant sheath material for optical cables according to claim 6, characterized in that: In step (2), the raw materials of the inner enhanced flame-retardant layer are mixed at 20-25℃ and 800 rpm for 5-10 minutes before extrusion, the melt-extrusion is performed by using a double-screw extruder, and the melt-extrusion temperature is 155-170℃ and the screw rotation speed is 180 rpm.

9. The method for preparing a flame-retardant sheath material for optical cables according to claim 6, characterized in that: In step (3), the extrusion temperature of the outer layer melt in the two extruders is 135-150°C, the extrusion temperature of the inner layer melt is 155-170°C, and the temperature of the double-layer co-extrusion die is 160°C; the length of the aramid short-cut fiber is 3-6 mm, and the aramid short-cut fiber is injected through a side weightless feeder at the end of the melting section and before the metering section of the inner layer extruder, and the vacuum degree of the vacuum setting is -0.07 MPa to -0.09 MPa.

10. An optical cable prepared from the flame-retardant sheath material according to any one of claims 1-5.