Total-cross-section flame-retardant optical cable and preparation method thereof

Abstract

The invention discloses a total-cross-section flame-retardant optical cable and a preparation method thereof, and belongs to the technical field of optical cables, the total-cross-section flame-retardant optical cable comprises a skeleton structure, the skeleton structure is provided with an accommodating groove along the axial direction, and an optical fiber unit is placed in the accommodating groove; the skeleton structure is prepared from a flame-retardant material; the periphery of the skeleton structure is coated with the water-blocking tape; and the outer sheath wraps the periphery of the water-blocking tape, and the outer sheath is made of a flame-retardant material. According to the total-cross-section flame-retardant optical cable, the internal skeleton structure, the outer sheath and the like of the optical cable are all made of flame-retardant materials, so that total-cross-section flame retardance of the optical cable is achieved. According to the total-cross-section flame-retardant optical cable, the flame-retardant capability of the optical cable can be greatly improved, the external sheath of the optical cable is flame-retardant, even if the external sheath is damaged, the internal main body skeleton structure can also be flame-retardant, and the problem that the optical cable is damaged due to internal combustion of a conventional optical cable is avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical cables, and particularly relates to a full-section flame-retardant optical cable and a preparation method thereof. BACKGROUND

[0002] With the demand for high density, high reliability and convenient construction of optical cables in 5G base station backhaul, fiber to the home and data center interconnection, skeleton type optical cables have become an important product in the field of optical fiber communication transmission. The skeleton type optical cable takes the central reinforcing member as the support, sets a spiral skeleton structure outside, embeds the optical fiber ribbon or single-core optical fiber into the groove of the skeleton structure, and then is wrapped with a water-blocking tape or an armor structure to form a special optical cable structure with excellent protection capability.

[0003] With the wide application of the skeleton type optical cable, in addition to the protection performance of the optical cable itself, the optical cable also has higher requirements for the flame-retardant performance in special scenes such as corridors, machine rooms, subways and power supplies. The conventional flame-retardant optical cable usually adopts a flame-retardant outer sheath to improve the flame-retardant performance of the optical cable. However, the inner unit structure of the flame-retardant optical cable cannot be prepared by using flame-retardant materials, and it is difficult to achieve full-section flame retardation. SUMMARY

[0004] In view of one or more of the above defects or improvement needs of the prior art, the application provides a full-section flame-retardant optical cable to solve the problem that the existing flame-retardant optical cable cannot achieve full-section flame retardation.

[0005] To achieve the above-mentioned purpose, the application provides a full-section flame-retardant optical cable, which comprises: a skeleton structure, the skeleton structure is provided with a containing groove along the axial direction, and an optical fiber unit is placed in the containing groove; wherein the skeleton structure is prepared by using a flame-retardant material; a water-blocking tape, the water-blocking tape is wrapped around the outer periphery of the skeleton structure; an outer sheath, the outer sheath is wrapped around the outer periphery of the water-blocking tape, and the outer sheath is prepared by using a flame-retardant material.

[0006] As a further improvement of the application, the skeleton structure is prepared by using polyethylene, and an additive flame-retardant agent is added to the skeleton structure.

[0007] As a further improvement of the application, a plasticizer and a lubricant are further added to the skeleton structure.

[0008] As a further improvement of the application, the additive flame-retardant agent is a combination of a phosphorus-based flame-retardant agent, an inorganic hydroxide flame-retardant agent and an inorganic metal flame-retardant agent.

[0009] As a further improvement of the application, the additive flame-retardant agent is a combination of red phosphorus, aluminum hydroxide, magnesium hydroxide and diantimony trioxide.

[0010] As a further improvement of the present application, the additive flame retardant comprises 10%~40% of red phosphorus, 20%~40% of aluminum hydroxide, 10%~20% of magnesium hydroxide and 10%~20% of antimony trioxide by mass ratio.

[0011] As a further improvement of the present application, the additive flame retardant satisfies the following material characteristics: At 200℃, 10s -1 The complex viscosity ratio Δη* (additive flame retardant / PE) of the additive flame retardant and the polyethylene melt at a shear rate of 10s-1 is ≤3.0; And the volume percolation threshold φc of the additive flame retardant in the polyethylene matrix is ≤0.20; The cumulative volume distribution Dv90 measured by laser particle size method is 1μm≤Dv90≤20μm, and the span Span= (Dv90-Dv10) / Dv50≤2.0; The difference |γsp-γPE| between the surface polarity component γsp of the additive flame retardant and the surface energy γPE of the polyethylene at 25℃, relative humidity 50% is ≤15 mN m -1 ; The 5% corresponding temperature Td5 of the thermal weight loss of the additive flame retardant in air at 300℃ is ≥240℃; And the total additive amount of the additive flame retardant accounts for 10%~40% of the total mass of the skeleton structure.

[0012] As a further improvement of the present application, the skeleton structure comprises a skeleton body, and a plurality of accommodation grooves are uniformly distributed around the skeleton body, and the plurality of accommodation grooves are arranged in a twisted manner along the axial direction of the skeleton body.

[0013] As a further improvement of the present application, the optical fiber unit is accommodated in the accommodation groove, and the twisted pitch of the optical fiber unit is 550mm~750mm.

[0014] As a further improvement of the present application, the optical fiber unit comprises a plurality of flame-retardant optical fibers, and the flame-retardant optical fiber comprises a core layer, a cladding layer and a double-layer coating, and the double-layer coating is composed of a polyimide inner layer and a silicone rubber outer layer.

[0015] As a further improvement of the present application, the optical fiber unit is accommodated in a sleeve, and the sleeve is embedded in the accommodation groove.

[0016] As a further improvement of the present application, the optical fiber unit is coated with a water-blocking yarn.

[0017] As a further improvement of the present application, the skeleton structure comprises a central support part, and a plurality of protruding parts are arranged circumferentially on the central support part, the plurality of protruding parts and the central support part jointly form the skeleton structure, and the accommodation grooves are formed between adjacent two protruding parts; the proportion of the added flame retardant in the central support part is lower than the proportion of the added flame retardant in the protruding parts.

[0018] As a further improvement of the present application, the skeleton structure comprises a central support part, and a plurality of protruding parts are arranged circumferentially on the central support part, the plurality of protruding parts and the central support part jointly form the skeleton structure, and the accommodation grooves are formed between adjacent two protruding parts; the modulus of polyethylene in the central support part is greater than the modulus of polyethylene in the protruding parts.

[0019] As a further improvement of the present application, the water-blocking tape is a fire-resistant water-blocking tape.

[0020] As a further improvement of the present application, the water-blocking tape is further coated with an armor layer.

[0021] The present application also comprises a preparation method of the full-section flame-retardant optical cable, which comprises the following steps: extruding the skeleton structure, and placing the optical fiber unit in the accommodation grooves of the skeleton structure; coating the water-blocking tape on the periphery of the skeleton structure, coating the armor layer on the periphery of the water-blocking tape, and extruding the outer sheath on the periphery of the armor layer to form the full-section flame-retardant optical cable; wherein the skeleton structure is formed by step-by-step extrusion: first, adding plasticizer and lubricant in the polyethylene sheath material, and then extruding and granulating to form the preliminary master batch; mixing and extruding the preliminary master batch with the added flame retardant to form the skeleton structure master granule; extruding and forming the skeleton structure by using an extruder.

[0022] As a further improvement of the present application, the optical fiber unit comprises a sleeve and a fiber bundle, and a water-blocking yarn is arranged between the sleeve and the fiber bundle.

[0023] As a further improvement of the present application, the sleeve is prepared by using flame-retardant TPE, flame-retardant TPU or flame-retardant PE.

[0024] As a further improvement of the present application, the plasticizer and the lubricant account for 3% to 30% of the weight of the polyethylene.

[0025] As a further improvement of the present application, the added flame retardant accounts for 10% to 30% of the weight of the preliminary master batch.

[0026] As a further improvement of the present application, the extrusion temperature of the skeleton structure is 150°C to 160°C.

[0027] The above technical features can be combined with each other as long as they do not conflict with each other.

[0028] In general, compared with the prior art, the above technical solutions conceived by the present application have the beneficial effects including: (1) The full-section flame-retardant optical cable of the present application can greatly improve the flame-retardant ability of the optical cable, and in addition to the flame-retardant optical cable external sheath, even if the external sheath is damaged, the internal main skeleton structure can also be flame-retardant, avoiding the problem of conventional optical cable damage caused by internal combustion.

[0029] (2) The full-section flame-retardant optical cable of the present application adds an additive flame retardant in the skeleton structure, and the additive flame retardant is a combination of red phosphorus, aluminum hydroxide, magnesium hydroxide and antimony trioxide. Among them, the aluminum hydroxide and magnesium hydroxide can wrap the red phosphorus to solve the problem of red phosphorus easy to absorb moisture and oxidation; at the same time, the magnesium hydroxide and aluminum hydroxide can perform superfine and surface modification treatment on the surface of polyethylene, so that the antimony trioxide is more uniformly dispersed in the polyethylene material, ensuring the flame-retardant effect, reducing the influence of inorganic metal flame retardant on the polyethylene forming skeleton structure, and reducing the wear of the extrusion equipment. The present application realizes full-stage flame-retardant of the skeleton structure by the combination of red phosphorus, aluminum hydroxide, magnesium hydroxide and antimony trioxide, greatly improves the flame-retardant ability of the skeleton structure, and facilitates the full-section flame-retardant optical cable to realize full-section flame-retardant.

[0030] (3) The preparation method of the full-section flame-retardant optical cable of the present application adopts a two-step modified extrusion method, first adding plasticizer and lubricant into the polyethylene sheath material to form a preliminary master batch; then adding an additive flame retardant into the preliminary master batch to form a skeleton structure master batch, and then extruding to prepare the skeleton structure; through the step-by-step modification method, the polyethylene, plasticizer and lubricant first form a proportion, and then the mixture of polyethylene, plasticizer and lubricant forms a proportion with the additive flame retardant, through two times of proportion amplification, the proportion of a small amount of plasticizer and lubricant relative to polyethylene can be controlled in a relatively accurate range, realizing accurate addition of plasticizer and lubricant, effectively ensuring the stable formation and flame-retardant performance of the skeleton structure; in addition, the separate addition of plasticizer and lubricant and additive flame retardant can avoid the interference between additive flame retardant and plasticizer and lubricant, and ensure the effective action of plasticizer, lubricant and additive flame retardant. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the overall structure schematic diagram of the full-section flame-retardant optical cable in the embodiment of the present application.

[0032] In all the drawings, the same reference signs represent the same technical features, specifically: 1, central reinforcement; 2, skeleton structure; 3, optical fiber unit; 4, water-blocking tape; 5, armor layer; 6, outer sheath. DETAILED DESCRIPTION

[0033] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0034] In the description of the present application, it should be understood that, unless otherwise specified, the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the purpose of facilitating the description of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0035] In addition, unless otherwise specified, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0036] In the present application, unless otherwise specifically specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise specifically limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0037] In the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature "on", "above" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the first feature is higher in horizontal height than the second feature. The first feature "under", "below" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the first feature is lower in horizontal height than the second feature.

[0038] Embodiment: Please refer to Figure 1 The full-section flame-retardant optical cable in the preferred embodiment of the present application comprises a skeleton structure 2, the skeleton structure 2 is provided with a containing groove in the axial direction, and an optical fiber unit 3 is placed in the containing groove; wherein the skeleton structure 2 is prepared from a flame-retardant material; a water-blocking belt 4 is wrapped around the outer periphery of the skeleton structure 2; and an outer sheath 6 is wrapped around the outer periphery of the water-blocking belt 4, and the outer sheath 6 is prepared from a flame-retardant material.

[0039] The full-section flame-retardant optical cable in the present application is prepared from a flame-retardant material for the internal skeleton structure 2 and the outer sheath 6 of the optical cable, so as to realize full-section flame retardation of the optical cable. The full-section flame-retardant optical cable can greatly improve the flame-retardant capability of the optical cable. In addition to the flame-retardant capability of the outer sheath of the optical cable, even if the optical cable is damaged, the internal main skeleton structure 2 can also be flame-retardant, thereby avoiding the problem that the conventional optical cable is damaged due to internal combustion.

[0040] Compared with other types of optical cables, the main difference of the skeleton optical cable is that a regular skeleton structure 2 is formed inside the skeleton optical cable. The skeleton structure 2 needs to have a higher strength, and the whole skeleton structure 2 needs to be regular. Regular grooves are formed on the skeleton for accommodating the optical fiber unit 3. The prior art does not have a flame-retardant skeleton structure 2. The main problem is that after the existing flame-retardant components are added to the skeleton structure 2, the difficulty of skeleton forming is increased, the skeleton is difficult to be extruded, and it is difficult to be formed into a regular skeleton structure 2. Based on this, the present application proposes a full-section flame-retardant skeleton optical cable, which realizes full-section flame retardation of the optical cable by preparing a flame-retardant skeleton structure 2.

[0041] Further, as an optional embodiment of the present application, the skeleton structure 2 in the present application is prepared from polyethylene, and the skeleton structure 2 further comprises an additive flame retardant. The additive flame retardant is mainly mixed into the base material through a physical mixing method, which can realize flame retardation without changing the molecular structure of the material. It can change the flame-retardant performance of the skeleton structure 2 without affecting the main performance of the skeleton structure 2. Moreover, based on the adding method of the additive flame retardant, the adding ratio can be directly controlled to change the flame-retardant performance, and the composition and type of the flame retardant are easier to adjust, which is suitable for the optical cable preparation process.

[0042] Further, as an optional embodiment of the present application, the plasticizer and lubricant are added to the skeleton structure 2. The addition of the flame-retardant component to the polyethylene causes the skeleton structure 2 to be difficult to extrude and to be difficult to shape. The plasticizer can improve the plasticity, flexibility and ductility of the polyethylene, reduce the viscosity of the polyethylene and improve the processing fluidity, so that the polyethylene is easier to mix and extrude. The lubricant can improve the processing fluidity and demolding performance of the polyethylene material, and improve the surface gloss of the skeleton structure 2. Therefore, the plasticizer and the lubricant are added to the skeleton structure 2 to improve the plasticity and extrusion performance of the skeleton structure 2.

[0043] Further, as an optional embodiment of the present application, the additive flame retardant in the present application is a combination of phosphorus-based flame retardant, inorganic hydroxide flame retardant and inorganic metal flame retardant. The flame retardant used in conventional optical cables is halogen-based flame retardant. The halogen-based flame retardant has high efficiency that is incomparable to other flame retardants, but it generates dense smoke and corrosive gas in the combustion process, which brings secondary disasters to human health and environment. Therefore, the combination structure of phosphorus-based flame retardant, inorganic hydroxide flame retardant and antimony trioxide is selected. The phosphorus-based flame retardant has good flame-retardant effect, and the generated metaphosphoric acid can be polymerized to form a stable polymeric state to form a protective layer of the skeleton structure 2, so as to isolate the skeleton structure 2 from oxygen and combustible materials. The phosphoric acid can promote the carbonization of the skeleton structure 2, and the carbonized structure can separate the skeleton structure 2 from the outside to slow down the burning rate of the skeleton structure 2. The inorganic metal flame retardant has the advantages of good thermal stability, non-toxicity, no corrosive gas, no volatilization, smoke suppression, long-lasting effect and low price. The inorganic hydroxide flame retardant contains a large number of hydroxyl groups in the molecular structure, which will undergo dehydration decomposition reaction to generate metal oxide and water after heating. The reaction process can absorb a large amount of heat to reduce the temperature of the skeleton structure 2. In addition, the generated metal oxide can form an inorganic protective layer on the outer layer of the skeleton structure 2 to block the oxygen and combustible materials, and the generated water vapor can reduce the oxygen concentration around the skeleton structure 2 to achieve flame retardation. The combination of the above three kinds of flame retardants can achieve the flame retardation of the skeleton structure 2.

[0044] Optionally, the inorganic hydroxide flame retardant in the present application is magnesium hydroxide and / or aluminum hydroxide. The aluminum hydroxide molecule contains up to 34% of chemically associated water, and it remains stable at the processing temperature of the skeleton structure 2. However, the aluminum hydroxide will decompose and release water vapor at a temperature above 200℃ to absorb the heat generated during combustion. The dehydration endothermic temperature of aluminum hydroxide is about 235℃-350℃, which can play a good flame-retardant effect when the skeleton structure 2 starts to burn, and has a lower smoke emission. Relatively speaking, the decomposition temperature of magnesium hydroxide is higher, which decomposes at about 340℃-490℃, and the heat absorption is smaller, but the carbonization flame-retardant effect of magnesium hydroxide on the skeleton structure 2 is better than that of aluminum hydroxide. By using a combination of magnesium hydroxide and aluminum hydroxide, different temperature ranges during combustion can be covered to achieve sustained flame retardation and smoke suppression.

[0045] Optionally, the phosphorus-based flame retardant in the present application is red phosphorus.

[0046] Optionally, the inorganic metal flame retardant in the present application is antimony trioxide. Polyethylene is easy to burn and will continue to burn after being away from the fire, so it is necessary to add antimony trioxide, which will produce a smothering gas (antimony oxynitride) when polyethylene burns to achieve flame retardation.

[0047] Optionally, the additive flame retardant in the present application is a combination of red phosphorus, aluminum hydroxide, magnesium hydroxide and antimony trioxide. Specifically, red phosphorus has good flame-retardant effect, but red phosphorus is easy to absorb moisture and oxidize, so aluminum hydroxide and magnesium hydroxide are used to wrap it to reduce the contact between red phosphorus and the external environment during the addition process, and to reduce water absorption and oxidation. In addition, although inorganic metal flame retardants have many advantages in flame retardation, they will affect the processing and molding properties and physical properties of polyethylene, so they need to be superfined and surface modified. The low-density polyethylene graft can modify the surface of nano-sized aluminum hydroxide and magnesium hydroxide, so that the inorganic metal flame retardant is more uniformly dispersed in the polyethylene material, thereby ensuring the flame-retardant effect, reducing the influence of inorganic metal flame retardant on the polyethylene molding skeleton structure 2, and reducing the wear on the extrusion equipment. The present application greatly improves the flame-retardant ability of the skeleton structure 2 by using a combination of red phosphorus, aluminum hydroxide, magnesium hydroxide and antimony trioxide, which facilitates the realization of full-section flame-retardant optical cable.

[0048] Further, as an optional embodiment of the present application, the additive flame retardant in the present application comprises 10% to 40% of red phosphorus, 20% to 40% of aluminum hydroxide, 10% to 20% of magnesium hydroxide, and 10% to 20% of antimony trioxide by mass ratio. Preferably, the diameter of the additive flame retardant is about 3 mm, the size variation of the additive flame retardant is within ±5%, and the particle size distribution of the additive flame retardant is: D10=2.9 mm, D50=3.0 mm, and D90=3.1 mm. The use of the additive flame retardant with the above-mentioned ratio enables the all-section flame-retardant optical cable in the present application to achieve a V0 flame-retardant level in the UL-94 standard.

[0049] Further, as an optional embodiment of the present application, the additive flame retardant generally satisfies the following material characteristics: at 200℃, 10s -1 1under the shear rate, the complex viscosity ratio Δη* (additive flame retardant / PE) of the additive flame retardant and the polyethylene melt is ≤3.0; the volume percolation threshold φc of the additive flame retardant in the polyethylene matrix is ≤0.20; the volume distribution cumulative Dv90 measured by the laser particle size method is 1 μm ≤ Dv90 ≤ 20 μm, and the span Span = (Dv90-Dv10) / Dv50 ≤ 2.0; under the condition of 25℃ and 50% relative humidity, the difference |γsp-γPE| between the surface polarity component γsp of the additive flame retardant and the surface energy γPE of the polyethylene is ≤ 15 mN·m -1 ; under the air atmosphere at 300℃, the 5% corresponding temperature Td5 of the thermal weight loss of the additive flame retardant is ≥240℃; and the total additive amount of the additive flame retardant accounts for 10% to 40% of the total mass of the skeleton structure 2.

[0050] The additive flame retardant in the present application is formed by combining and proportioning red phosphorus, aluminum hydroxide, magnesium hydroxide, and antimony trioxide. Among them, the aluminum hydroxide and the magnesium hydroxide are used as hard nano-carriers to coat the surface of the red phosphorus to form a core-shell structure with a thickness of 5 to 15 nm and an electric potential of not less than 30 mV, which ensures the electrostatic repulsion and steric hindrance synergy of the additive flame retardant in the polyethylene matrix; at the same time, the antimony trioxide is pretreated by a silane coupling agent, the grafting rate is 1.2% to 2.0%, the surface energy can be reduced to 28 mN·m -1 , the Flory-Huggins χ parameter of the additive flame retardant and the polyethylene melt is reduced from about 0.82 to about 0.35, and the nanoscale monodisperse (D90 ≤ 3.1 μm) can be realized. The steady distribution of the additive flame retardant in the polyethylene melt satisfies the Gibbs mixing free energy, and the nanometer network of the core-shell structure and the antimony trioxide synergizes at 200℃, 10s -1The percolation threshold φc≤0.20 is formed in the extrusion field under the shear rate, which is lower than the percolation threshold of the classical percolation model, while the complex viscosity of the skeleton structure 2 is in a controllable range, which ensures the flowability of the material of the skeleton structure 2 and realizes the material balance between the flame retardation and the extrusion molding of the skeleton structure 2.

[0051] Further, as an optional embodiment of the present application, the skeleton structure 2 in the present application comprises a skeleton body, and a plurality of accommodation grooves are uniformly distributed around the skeleton body and are arranged in a twisted manner along the axial direction of the skeleton body. The accommodation grooves are arranged in a twisted structure, so that the optical fiber units 3 in the accommodation grooves are also arranged in a twisted structure, which can significantly improve the tensile and bending resistance of the optical fiber. Optionally, the accommodation grooves on the skeleton structure 2 can form S-twisted, Z-twisted or SZ-twisted grooves.

[0052] Optionally, the twisted pitch of the optical fiber unit 3 in the present application is 550mm-750mm. The twisted pitch of the conventional skeleton optical cable is 400mm-500mm. The twisted pitch in the present application is longer than that of the conventional skeleton optical cable, so that the twisting amplitude of the skeleton structure 2 can be reduced, the molding difficulty of the skeleton structure 2 is reduced, and the molding of the full-section flame-retardant optical cable is facilitated.

[0053] Further, as an optional embodiment of the present application, the accommodation grooves on the skeleton structure 2 in the present application can be trapezoidal grooves, rectangular grooves or C-shaped grooves. Optionally, 1-6 optical fiber units 3 are placed in the accommodation grooves of the skeleton structure 2.

[0054] Further, as an optional embodiment of the present application, the optical fiber unit 3 in the present application comprises a plurality of flame-retardant optical fibers, which comprise a core layer, a cladding layer and a double-layer coating, and the double-layer coating comprises a polyimide inner layer and a silicone rubber outer layer. The polyimide contains a high-temperature-resistant aromatic ring and an imide bond, which will preferentially carbonize to form a dense carbon layer at high temperature. The carbon layer has stable structure and low thermal conductivity, which can physically isolate the flame from the optical fiber substrate and prevent heat transfer to the inside. Secondly, the silicone rubber will form a silica inorganic protective layer when burning, which can cover the surface of the carbon layer, further enhancing the isolation effect of the internal and external oxygen and heat of the optical fiber unit 3, forming a double-layer flame-retardant structure. Secondly, the high strength and high temperature resistance of polyimide can compensate for the softening defect of silicone rubber at high temperature, ensuring the integrity of the coating structure; and the flexibility and flame retardance of silicone rubber can improve the brittleness of polyimide and avoid the flame retardation failure caused by local rupture of polyimide when burning.

[0055] Further, as an optional embodiment of the present application, the optical fiber unit 3 in the present application is accommodated in the sleeve, and the sleeve is embedded in the accommodating groove of the framework structure 2. Alternatively, the sleeve is also made of flame-retardant material, and the sleeve is made of flame-retardant TPU, flame-retardant TPE or flame-retardant PE. When the sleeve is used, water-blocking yarn or water-blocking powder can also be added between the optical fiber unit and the sleeve. When the additive flame-retardant is added in the polyethylene, the formed framework structure 2 is also affected, and the surface of the framework structure 2 containing the flame-retardant is not as smooth as the traditional framework structure 2. In order to avoid that the inner wall of the accommodating groove of the framework structure 2 is too rough, which causes the outer coating of the optical fiber unit 3 to be scratched, and causes the optical fiber unit 3 to be damaged or the additional attenuation to increase, the present application additionally provides a sleeve structure outside the optical fiber unit 3, and a buffer is formed between the optical fiber unit 3 and the framework structure 2 through the sleeve, so as to reduce the forming requirement of the framework unit. Specifically, the attenuation level of the full-section flame-retardant optical cable in the present application is shown in the following table:

[0056] It can be seen that the attenuation coefficient of the full-section flame-retardant optical cable structure in the present application under different wave bands is connected with the conventional framework optical cable, which realizes the full-section flame-retardant of the optical cable under the premise of meeting the normal use of the optical cable.

[0057] Further, as an optional embodiment of the present application, the optical fiber unit 3 in the present application is accommodated in the sleeve, and the sleeve is embedded in the accommodating groove of the framework structure 2. Alternatively, the sleeve is also made of flame-retardant material, and the sleeve is made of flame-retardant TPU, flame-retardant TPE or flame-retardant PE. When the sleeve is used, water-blocking yarn or water-blocking powder can also be added between the optical fiber unit and the sleeve. When the additive flame-retardant is added in the polyethylene, the formed framework structure 2 is also affected, and the surface of the framework structure 2 containing the flame-retardant is not as smooth as the traditional framework structure 2. In order to avoid that the inner wall of the accommodating groove of the framework structure 2 is too rough, which causes the outer coating of the optical fiber unit 3 to be scratched, and causes the optical fiber unit 3 to be damaged or the additional attenuation to increase, the present application additionally provides a sleeve structure outside the optical fiber unit 3, and a buffer is formed between the optical fiber unit 3 and the framework structure 2 through the sleeve, so as to reduce the forming requirement of the framework unit. Specifically, the attenuation level of the full-section flame-retardant optical cable in the present application is shown in the following table: Further, as an optional embodiment of the present application, the axial center of the framework structure 2 is also provided with a center reinforcing member 1. The center reinforcing member 1 can improve the tensile and bending resistance of the framework structure 2, and can avoid the shrinkage, deformation and collapse of the framework structure 2 caused by the change of external environment in the long-term use process, and improve the overall stability of the framework structure 2.

[0058] Further, as an optional embodiment of the present application, the framework structure 2 in the present application comprises a central support part, a plurality of protruding parts are arranged on the circumference of the central support part, the plurality of protruding parts and the central support part jointly form the framework structure 2, and a containing groove is formed between adjacent two protruding parts; and the proportion of the added flame retardant in the central support part is lower than the proportion of the added flame retardant in the protruding part. Optionally, the proportion of the added flame retardant to polyethylene in the central support part is 1:3-1:10; and the proportion of the added flame retardant to polyethylene in the protruding part is 1:2-1:8. The framework structure 2 is mainly used for resisting tension, compression and bending. When the framework structure 2 is divided into the central support part and the protruding part, the protruding part is located outside the central support part, and the flame retardant demand of the protruding part is higher. In addition, the protruding part is mainly used for forming the containing groove, and the demand for the shape and size of the protruding part itself is lower than that of the central support part. Therefore, by adjusting the proportion of the added flame retardant in the central support part and the protruding part, the shape regularity of part of the protruding part is sacrificed, and the overall flame retardation of the framework structure 2 is ensured.

[0059] Further, as an optional embodiment of the present application, the framework structure 2 in the present application comprises a central support part, a plurality of protruding parts are arranged on the circumference of the central support part, the plurality of protruding parts and the central support part jointly form the framework structure 2, and a containing groove is formed between adjacent two protruding parts; and the proportion of the added flame retardant in the central support part is lower than the proportion of the added flame retardant in the protruding part. Optionally, the proportion of the added flame retardant to polyethylene in the central support part is 1:3-1:10; and the proportion of the added flame retardant to polyethylene in the protruding part is 1:2-1:8. The framework structure 2 is mainly used for resisting tension, compression and bending. When the framework structure 2 is divided into the central support part and the protruding part, the protruding part is located outside the central support part, and the flame retardant demand of the protruding part is higher. In addition, the protruding part is mainly used for forming the containing groove, and the demand for the shape and size of the protruding part itself is lower than that of the central support part. Therefore, by adjusting the proportion of the added flame retardant in the central support part and the protruding part, the shape regularity of part of the protruding part is sacrificed, and the overall flame retardation of the framework structure 2 is ensured.

[0060] Further, as an optional embodiment of the present application, the framework structure 2 in the present application comprises a central support part, a plurality of protruding parts are arranged on the circumference of the central support part, the plurality of protruding parts and the central support part jointly form the framework structure 2, and a containing groove is formed between adjacent two protruding parts; and the proportion of the added flame retardant in the central support part is lower than the proportion of the added flame retardant in the protruding part. Optionally, the proportion of the added flame retardant to polyethylene in the central support part is 1:3-1:10; and the proportion of the added flame retardant to polyethylene in the protruding part is 1:2-1:8. The framework structure 2 is mainly used for resisting tension, compression and bending. When the framework structure 2 is divided into the central support part and the protruding part, the protruding part is located outside the central support part, and the flame retardant demand of the protruding part is higher. In addition, the protruding part is mainly used for forming the containing groove, and the demand for the shape and size of the protruding part itself is lower than that of the central support part. Therefore, by adjusting the proportion of the added flame retardant in the central support part and the protruding part, the shape regularity of part of the protruding part is sacrificed, and the overall flame retardation of the framework structure 2 is ensured. -1The complex viscosity ratio of the additive flame retardant and the polyethylene melt at the shear rate is Δη 2 *, and Δη 1 * : Δη 2 * is 60%~80%. -1 The complex viscosity ratio of the additive flame retardant and the polyethylene melt at the shear rate is Δη 2 *, and Δη 1 * : Δη 2 * is 60%~80%.

[0061] Further, as an optional embodiment of the present application, the water-blocking tape 4 in the present application is a fire-resistant water-blocking tape 4. The substrate of the water-blocking tape 4 is a polyester film, a non-woven fabric or a glass fiber cloth, and a fire-resistant material and a water-blocking material are coated on the outer periphery of the substrate, respectively. The fire-resistant material is magnesium hydroxide, aluminum hydroxide, ceramic material or intumescent fire retardant coating, and the water-blocking material is water-absorbing resin or water-blocking glue coating. Alternatively, the substrate, the fire-resistant material and the water-blocking material are integrally bonded by hot melt adhesive.

[0062] Further, as an optional embodiment of the present application, the outer periphery of the water-blocking tape 4 in the present application is further coated with an armor layer 5. The armor layer 5 can increase the overall structural rigidity of the optical cable and improve the water-blocking performance of the optical cable. Alternatively, the armor layer 5 is an aluminum strip or a steel strip, preferably a steel strip.

[0063] Further, as an optional embodiment of the present application, the outer jacket 6 in the present application is a flame-retardant polyethylene outer jacket 6. The flame-retardant component in the outer jacket 6 can be one or more of magnesium hydroxide, aluminum hydroxide, ammonium polyphosphate and halogen flame retardant. The addition of the flame-retardant component in the polyethylene jacket is a relatively common design in the field, and will not be repeated here.

[0064] Further, as an optional embodiment of the present application, the diameter of the skeleton structure 2 in the present application is 3mm~16mm, and the skeleton structure 2 has 2~15 accommodation grooves; each optical fiber unit 3 contains 1~24 optical fibers, and the diameter of the optical fiber unit 3 is 0.8mm~2.0mm; the overall full-section flame-retardant optical cable in the present application contains 1~288 optical fibers, and the overall diameter of the optical cable is 8mm~21mm.

[0065] The full-section flame-retardant optical cable in the present application realizes full-section flame-retardant of the optical cable by setting the full-section flame-retardant structure, and sets the coating of the optical fiber unit 3, the skeleton structure 2, the water-blocking tape 4 and the outer jacket 6 as flame-retardant materials, which greatly improves the flame-retardant performance of the optical cable; at the same time, the skeleton optical cable structure in the present application realizes high lateral pressure resistance grade of the optical cable by the cooperation of the skeleton structure 2 and the armor layer 5, which improves the lateral pressure resistance of the optical cable from 3000N / m of the traditional to 7000N / m; in addition, the full-section flame-retardant optical cable in the present application is a full-dry structure, has no ointment inside, has low combustion smoke density, and has small overall size, which can effectively reduce the cost of the optical cable.

[0066] Further, the application also includes a preparation method of the full-section flame-retardant optical cable, which comprises the following steps: extruding the framework structure 2, placing the optical fiber unit 3 along the accommodating groove of the framework structure 2; coating the waterproof belt 4 on the periphery of the framework structure 2, coating the armor layer 5 on the periphery of the waterproof belt 4, and extruding the outer sheath 6 on the periphery of the armor layer 5 to form the full-section flame-retardant optical cable; The framework structure 2 is formed by step-by-step extrusion: first, plasticizers and lubricants are added to the polyethylene sheath material, and then the material is extruded and granulated to form a preliminary master batch; the particle size of the preliminary master batch is about 3 mm, and the size variation is within ±5%, wherein D10=2.9 mm, D50=3.0 mm, and D90=3.1 mm; The preliminary master batch is mixed with the additive flame retardant to form the framework structure 2 master batch; The framework structure 2 is formed by using an extruder.

[0067] The preparation method of the full-section flame-retardant optical cable in the application adopts a two-step modified extrusion method: first, plasticizers and lubricants are added to the polyethylene sheath material to form a preliminary master batch; then, the additive flame retardant is added to the preliminary master batch to form the framework structure 2 master batch, and then the framework structure 2 is extruded; through the step-by-step modification method, the polyethylene, plasticizers and lubricants first form a proportion, and then the mixture of polyethylene, plasticizers and lubricants forms a proportion with the additive flame retardant, so that the proportion of a small amount of plasticizers and lubricants to polyethylene can be controlled within a relatively accurate range, the accurate addition of plasticizers and lubricants is realized, and the stable formation and flame-retardant performance of the framework structure 2 are effectively ensured; in addition, the separate addition of plasticizers, lubricants and additive flame retardants can avoid the interference between the additive flame retardant and the above-mentioned plasticizers and lubricants, and ensure the effective action of the plasticizers, lubricants and additive flame retardant.

[0068] Further, as an optional embodiment of the application, the mass ratio of the plasticizers and lubricants to the polyethylene in the application is 3% to 30%.

[0069] Further, as an optional embodiment of the application, the mass ratio of the additive flame retardant to the preliminary master batch in the application is 10% to 30%. The dispersion coefficient of the mixed master batch is 0.02% to 0.05%, which proves that the preliminary master batch and the polyethylene particles form a mixed master batch with good uniformity.

[0070] Further, as an optional embodiment of the application, the plasticizers in the application are polyolefin elastomers and ethylene-vinyl acetate copolymers.

[0071] Further, as an optional embodiment of the present application, the lubricant in the present application is silicone master batch, polyethylene wax, zinc stearate or oleic acid amide.

[0072] Further, as an optional embodiment of the present application, when the extruder is used to extrude the skeleton structure 2, the extrusion temperature of the extruder is 150-160°C. The extrusion temperature of the conventional polyethylene skeleton is 170-180°C. In comparison, the extrusion temperature of the skeleton structure 2 is lower than the conventional extrusion temperature. The lower extrusion temperature reduces the flowability of the polyethylene, and the polyethylene has a better molding effect, which is convenient for the skeleton structure 2 to be molded into a set shape. The following different size optical cable structures are prepared by using the optical cable preparation method of the present application, and the smoke density of the optical cable is tested under the condition of oxygen index 18. The specific test results are as follows:

[0073] Further, the conventional polyethylene skeleton is used to form a non-full-section flame-retardant cable, and the smoke density of the optical cable is tested under the condition of oxygen index 18. The specific test results are as follows:

[0074] From the above comparison, it can be seen that the full-section flame-retardant optical cable prepared by using the flame-retardant material can improve the flame-retardant grade of the optical cable under the full size. The flame-retardant performance of the full-section flame-retardant optical cable of the present application can reach the V0 flame-retardant grade in the UL-94 standard. In comparison, the flame-retardant performance of the conventional polyethylene skeleton optical cable structure can only reach the V2 flame-retardant grade in the UL-94 standard.

[0075] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A full-faceted flame-retardant optical cable characterized by, include: A skeleton structure having an axially oriented accommodating groove, wherein an optical fiber unit is placed within the accommodating groove; wherein the skeleton structure is made of flame-retardant material. A water-blocking strip, which covers the outer periphery of the skeleton structure; An outer sheath, which covers the outer periphery of the water-blocking strip, is made of flame-retardant material.

2. The full-faceted flame-retardant optical cable according to claim 1, wherein The skeleton structure is made of polyethylene and contains an additive flame retardant.

3. The full-faceted flame-retardant optical cable of claim 2, wherein Plasticizers and lubricants are also added to the skeleton structure.

4. The full-faceted flame-retardant optical cable of claim 2, wherein The additive flame retardant is a combination of phosphorus-based flame retardants, inorganic hydroxide flame retardants, and inorganic metal flame retardants.

5. The full-faceted flame-retardant optical cable of claim 4, wherein, The additive flame retardant is a combination of red phosphorus, aluminum hydroxide, magnesium hydroxide, and antimony trioxide.

6. The full-faceted flame-retardant optical cable according to claim 5, wherein The additive flame retardant comprises, by mass ratio, 10% to 40% red phosphorus, 20% to 40% aluminum hydroxide, 10% to 20% magnesium hydroxide, and 10% to 20% antimony trioxide.

7. The full-faceted flame-retardant optical cable of claim 6, wherein The additive flame retardant meets the following material characteristics: At 200°C, 10 s -1 The complex viscosity ratio Δη* (additive flame retardant / PE) of the additive flame retardant to the polyethylene melt is ≤ 3.0 at a shear rate of 10 s Furthermore, the volumetric percolation threshold φc of the added flame retardant in the polyethylene matrix is ​​≤0.20; The cumulative volume distribution Dv90 measured by the laser particle size distribution method is 1μm≤Dv90≤20μm, and the span Span=(Dv90-Dv10) / Dv50≤2.0; the difference | ysp- yPE| between the surface polar component ysp of the additive flame retardant and the surface energy yPE of the polyethylene is ≤ 15 mN m at 25°C, relative humidity 50% -1 ; In an air atmosphere at 300°C, the temperature Td5 corresponding to a 5% thermal weight loss of the additive flame retardant is ≥240°C. Furthermore, the total amount of the added flame retardant accounts for 10% to 40% of the total mass of the skeleton structure.

8. The fully jacketed flame retardant optical fiber cable of any of claims 1-7, wherein, The skeleton structure includes a skeleton body, and the skeleton body has a plurality of accommodating slots evenly distributed around its circumference. The plurality of accommodating slots are arranged to be twisted together along the axial direction of the skeleton body.

9. The full-faceted flame-retardant optical cable of claim 8, wherein, The optical fiber unit is housed within the receiving slot, and the twist pitch of the optical fiber unit is 550mm~750mm.

10. The fully jacketed flame retardant optical cable according to any one of claims 1 to 7, characterized in that, The optical fiber unit includes multiple flame-retardant optical fibers, each comprising a core layer, a cladding layer, and a double-layer coating. The double-layer coating consists of a polyimide inner layer and a silicone rubber outer layer.

11. The full-faceted flame-retardant optical cable according to any one of claims 1 to 7, characterized in that, The optical fiber unit is housed within a sleeve, and the sleeve is embedded within the receiving groove.

12. The full-faceted flame-retardant optical cable according to any one of claims 1 to 7, characterized by The outer periphery of the optical fiber unit is covered with water-blocking yarn.

13. The full-faceted flame-retardant optical cable according to any one of claims 1 to 7, characterized in that, The skeleton structure includes a central support portion, and the central support portion is provided with multiple protrusions in its circumference. The multiple protrusions and the central support portion together form the skeleton structure, and the receiving groove is formed between two adjacent protrusions. The proportion of additive flame retardant in the central support portion is lower than the proportion of additive flame retardant in the protrusions.

14. The full-faceted flame-retardant optical cable according to any one of claims 1 to 7, characterized by The skeleton structure includes a central support portion, and the central support portion is provided with a plurality of protrusions in the circumferential direction. The plurality of protrusions and the central support portion together form the skeleton structure, and the receiving groove is formed between two adjacent protrusions. The polyethylene modulus in the central support portion is greater than the polyethylene modulus in the protrusions.

15. The fully jacketed flame retardant optical fiber cable of any of claims 1-7, wherein, The water-blocking strip is a fire-resistant water-blocking strip.

16. The full-faceted flame-retardant optical cable according to any one of claims 1 to 7, characterized by The water-blocking strip is also covered with an armor layer on its outer periphery.

17. A method of making a full-faceted fire resistant optical cable, characterized by, Includes the following steps: Extrude the skeleton structure and place the optical fiber unit along the receiving groove of the skeleton structure; A water-blocking strip is wrapped around the outer periphery of the skeleton structure, an armor layer is wrapped around the outer periphery of the water-blocking strip, and an outer sheath is extruded around the outer periphery of the armor layer to form a full-section flame-retardant optical cable. The skeleton structure is step by step extruded, wherein, first, the plasticizer and lubricant are added into the polyethylene sheath material, and then the material is extruded and granulated to form a preliminary master batch; The preliminary master batch is mixed with the additive flame retardant and then extruded and granulated to form a skeleton structure master batch; The skeleton structure is extruded by an extruder.

18. The method of making a full-faceted flame-retardant optical cable of claim 17, wherein, The plasticizer and lubricant account for 3% to 30% of the weight of the polyethylene.

19. The method of claim 17, wherein the flame-retardant optical cable is a full- buffered cable. The additive flame retardant accounts for 10% to 30% of the weight of the preliminary master batch.

20. The method of claim 17, wherein the flame-retardant optical cable is a full- buffered cable. The extrusion temperature of the skeleton structure is 150℃ to 160℃.

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